10 100 1,000

Resistivity

ohm-m

From 

induction

tool

16-in.

normal

0

20

40

60

80

100Depth in meters

100 200

Gamma

cps

500 1,000 1,500

Neutron

cps

SP

-50 0

mV

0

50

150

200

250

300

Depth in feet 100

?

50

150

200

250

300

100

Depth in feet 0

Elevation

7,549 ft

(2,301 m)

Electrical

conductor

Prepared in cooperation with National Park Service

Sample Descriptions and Geophysical Logs 

for Cored Well BP-3-USGS, Great Sand Dunes 

National Park, Alamosa County, Colorado

Data Series 918

U.S. Department of the Interior

U.S. Geological Survey
Cover. Selected generalized geophysical logs and generalized lithologic logs for BP-3-USGS.

Photographs from top to bottom: 

 At the end of a core run, the barrel is lifted out of the hole onto one of the several sawhorse setups.

 Clay from the same sample as in A after almost 5 years of storage in a plastic bag.

 Stream of water that was flowing out of the drill stem into the mud pool the morning of September 17, 2009.

 Clay with blue tint at time of collection as a core catcher sample at 266 ft depth (core run 19). B, Clay with 

 even-gray color at time of collection from ≈311 ft depth (core run 26).

 Intact core after extrusion onto a split half of polyvinyl chloride pipe on a sawhorse apparatus.
Sample Descriptions and Geophysical Logs 

for Cored Well BP-3-USGS, Great Sand 

Dunes National Park, Alamosa County, 

Colorado

By V.J.S. Grauch, Gary L. Skipp, Jonathan V. Thomas, Joshua K. Davis, and 

Mary Ellen Benson

Prepared in cooperation with National Park Service

Data Series 918

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

SALLY JEWELL, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2015

For more information on the USGS—the Federal source for science about the Earth, its natural and living 

resources, natural hazards, and the environment—visit http://www.usgs.gov or call 1–888–ASK–USGS.

For an overview of USGS information products, including maps, imagery, and publications, 

visit http://www.usgs.gov/pubprod/.

Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the 

U.S. Government.

Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials 

as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner.

Suggested citation:

Grauch, V.J.S., Skipp, G.L., Thomas, J.V., Davis, J.K., and Benson, M.E., 2015, Sample descriptions and geophysical 

logs for cored well BP-3-USGS, Great Sand Dunes National Park and Preserve, Alamosa County, Colorado: 

U.S. Geological Survey Data Series 918, 53 p., http://dx.doi.org/10.3133/ds918.

ISSN 2327-638X (online)
iii

Contents

Abstract...........................................................................................................................................................1

Introduction.....................................................................................................................................................1

Regional Setting and Geophysical Studies ...............................................................................................3

Drilling Operations.........................................................................................................................................4

Procedures for Lithologic Descriptions .....................................................................................................6

Sampling Procedures...........................................................................................................................6

Mud Stream Samples..................................................................................................................6

Core Barrel Samples ...................................................................................................................6

Effects of Storage and Handling ......................................................................................................10

Laboratory Methods...........................................................................................................................13

Sample Descriptions Versus Well Depths......................................................................................13

Geophysical Logs.........................................................................................................................................16

Logs Acquired......................................................................................................................................16

Data Processing..................................................................................................................................16

Check of Depth Calibration ......................................................................................................18

Normal Resistivity Logs ............................................................................................................21

Induction Log..............................................................................................................................21

Density and Sonic Logs ............................................................................................................21

Digital Log Files ...................................................................................................................................26

Summary of Findings...................................................................................................................................26

Significance for Future Studies.................................................................................................................28

Acknowledgments.......................................................................................................................................30

References Cited..........................................................................................................................................30

Figures

1. Map showing location of BP-3-USGS well, the inferred limit of the last high stand of

Pliocene and Pleistocene Lake Alamosa before its disappearance and the Hansen

Bluff core site near Great Sand Dunes National Park and Preserve in Alamosa

County of southern Colorado ......................................................................................................3

2. Photographs of drilling operations ............................................................................................5

3. Photographs of various sampling procedures for mud stream samples ............................8

4. Photographs of various sampling procedures for core barrel samples .............................9

5. Photographs of a selected core at time of collection compared to more than 

4 years later.................................................................................................................................11

6. Photographs of two clay samples of differing color at time of collection in

September 2009 compared to almost 5 years later in August 2014....................................12

7. Graphical summary of lithologic descriptions and other observations versus

inferred well depth .....................................................................................................................14

8. Diagram showing borehole diameter measured by the three-arm caliper and

low-pass-filtered, natural gamma-ray curves from five different tools ............................19

9. Diagram showing comparison of original neutron curve to induction and

spontaneous potential logs to correct the depth scale for the neutron log.....................20
iv

10. Diagram showing normal resistivity curves from the multiparameter tool before and

after data processing.................................................................................................................22

11. Diagram showing resistivity derived from the induction tool before and after data

processing compared to normal resistivity curves after data processing.......................23

12. Diagram showing resistivity curves after data processing compared to resistivity

layers derived from a time-domain electromagnetic sounding measured at the site

before drilling ..............................................................................................................................24

13. Diagram showing sonic velocity and compensated density logs ......................................25

14. Diagram showing selected geophysical logs and generalized lithologic log for

BP-3-USGS...................................................................................................................................27

Tables

1. Explanation of and procedures for different sample types ...................................................7

2. Core lengths recovered onsite in 2009 and changes in measured lengths in years

2012 and 2013...............................................................................................................................10

3. Geophysical tools and associated data logs acquired for BP-3-USGS, listed in the

order they were acquired..........................................................................................................16

4. Description of geophysical logs and their utility for BP-3-USGS .......................................17

5. Overview of data processing steps applied to geophysical logs.......................................18

Appendix Tables

1. Descriptions of samples by type and drilling interval...........................................................34

2. Depth intervals where fossils or other evidence of life were observed ...........................47

3. Results of analysis by X-ray powder diffraction ...................................................................53

Download Files

Log files—data for borehole geophysical logs 

http://pubs.usgs.gov/ds/0918/downloads/LogFiles/

Photographs of samples taken onsite 

http://pubs.usgs.gov/ds/0918/downloads/PhotoFiles/
v

Conversion Factors

Inch/Pound to SI

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.60934 kilometer (km)

Density

grams per cubic centimeter (g/cm3) 1,000.0 kilograms per cubic meter (kg/m3)

Velocity

foot per second (ft/s) 0.3048 meter per second (m/s)

Flow rate

gallon per minute (gal/min) 0.06309 liter per second (L/s)

Electrical resistivity

ohm-meters (ohm-m) 0.001 kiloohm-meters (kohm-m)

Electrical conductivity

millimhos per meter (mmhos/m) 1,000.0 siemens per meter (S/m)

Electrical potential

millivolts (mV) 1,000.0 volts (V)

Supplemental Information

Electrical resistivity ρ in ohm-meters (ohm-m) can be converted to electrical conductivity σ in 

siemens per meter (S/m) as follows: σ = 1/ρ.

Datums

Vertical coordinate information is referenced to the North American Vertical Datum of 1988 

(NAVD 88).

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83).

Elevation, as used in this report, refers to distance above the vertical datum.
vi

Abbreviations Used in This Report

cps counts per second

EM electromagnetic

ka kilo-annum (thousand years)

Ma Mega-annum (million years)

NPS National Park Service

PVC polyvinyl chloride

TEM time-domain electromagnetic

USGS U.S. Geological Survey
Introduction 1

Sample Descriptions and Geophysical Logs for Cored 

Well BP-3-USGS, Great Sand Dunes National Park, 

Alamosa County, Colorado

By V.J.S. Grauch,1 Gary L. Skipp,1 Jonathan V. Thomas,1 Joshua K. Davis,2 and Mary Ellen Benson1

1

U.S. Geological Survey.

2

University of Texas at Austin.

Abstract

The BP-3-USGS well was drilled at the southwestern 

corner of Great Sand Dunes National Park in the San Luis 

Valley, south-central Colorado, 68 feet (ft, 20.7 meters [m]) 

southwest of the National Park Service’s boundary-piezometer 

(BP) well 3. BP-3-USGS is located at latitude 37°43ʹ18.06ʺN. 

and longitude 105°43ʹ39.30ʺW., at an elevation of 7,549 ft 

(2,301 m). The well was drilled through poorly consolidated sediments to a depth of 326 ft (99.4 m) in September 

2009. Water began flowing from the well after penetrating a 

clay-rich layer that was first intercepted at a depth of 119 ft 

(36.3 m). The base of this layer, at an elevation of 7,415 ft 

(2,260 m) above sea level, likely marks the top of a regional 

confined aquifer recognized throughout much of the San Luis 

Valley. Approximately 69 ft (21 m) of core was recovered 

(about 21 percent), almost exclusively from clay-rich zones. 

Coarser grained fractions were collected from mud extruded 

from the core barrel or captured from upwelling drilling fluids. 

Natural gamma-ray, full waveform sonic, density, neutron, 

resistivity, spontaneous potential, and induction logs were 

acquired. The well is now plugged and abandoned.

This report presents lithologic descriptions from the well 

samples and core, along with a compilation and basic data processing of the geophysical logs. The succession of sediments 

in the well can be generalized into three lithologic packages: 

(1) mostly sand from the surface to about 77 ft (23.5 m) depth; 

(2) interbedded sand, silt, and clay, decreasing in overall grain 

size downward, from 77 to 232 ft (23.5 to 70.7 m) depth; and 

(3) layers of massive clay alternating with layers of fine sand 

to silt from 232 to 326 ft (70.7 to 99.4 m), the total depth of 

the well. The topmost clay layers of the deepest package have 

a blue tint, prompting a correlation with the “blue clay” of the 

San Luis Valley that is commonly considered as the top of the 

confined aquifer. However, a confining clay was intercepted 

113 ft (34.4 m) higher than the blue clay in BP-3-USGS.

Most of the geophysical logs have good correspondence 

to the lithologic variations in the well. Exceptions are the 

gamma-ray log, which is likely affected by naturally occurring 

radiation from abundant volcanic detritus, and one interval 

within the deepest lithologic package, which appears to be 

abnormally electrically conductive. Resistivity logs and variations in sand versus clay content within the well are consistent 

with electrical resistivity models derived from time-domain 

electromagnetic geophysical surveys for the area. In particular, the topmost blue clay corresponds to a strong electrical 

conductor that is prominent in the electromagnetic geophysical 

data throughout the park and vicinity.

BP-3-USGS was sited to test hypotheses developed from 

geophysical studies and to answer questions about the history and evolution of Pliocene and Pleistocene Lake Alamosa, 

which is represented by lacustrine deposits sampled by the 

well. The findings reported here represent a basis from which 

future studies can answer these questions and address other 

important scientific questions in the San Luis Valley regarding 

geologic history and climate change, groundwater hydrology, 

and geophysical interpretation.

Introduction

The U.S. Geological Survey (USGS) has been conducting geologic and geophysical studies for several years in the 

San Luis Valley, Colorado, under the auspices of the National 

Cooperative Geologic Mapping Program. The goals are to 

improve understanding of the present-day geologic framework 

in three dimensions and its geologic history. A combination 

of drill-hole information, geophysical methods, and geologic mapping provide the most comprehensive approach to 

determining the third dimension of geology that underlies the 

landscape.

One focus of the USGS studies has centered on the 

evolution and nature of deposits left behind by a large lake 

that occupied most of the San Luis Valley in the Pliocene and 

Pleistocene (Siebenthal, 1910). Recent geologic investigations conclude that this ancient Lake Alamosa formed about 
2 Sample Descriptions and Geophysical Logs for Cored Well, Great Sand Dunes National Park, Colorado

3 million years ago when lava erupted onto the valley floor 

and created a dam (Machette and others, 2013). The lake eventually breached the dam and drained out to form the throughgoing, modern Rio Grande drainage system several thousand 

years ago (Machette and others, 2007, 2013). However, the 

exact timing and nature of the lake’s demise are still debated 

(Madole and others, 2013).

The deposits from the lake, known as the Alamosa 

Formation, include massive clay layers colloquially known as 

the “blue clay” that are penetrated by water wells throughout 

the San Luis Valley (Huntley, 1979a). The clays form barriers 

to groundwater flow, so they are important for understanding 

groundwater resources of the San Luis Valley, the primary 

water supply for its thriving agricultural community. Water 

resource managers in the valley use the depth and extent of 

the clays to define regulations for well pumping from an upper 

unconfined aquifer versus a lower confined aquifer. Knowledge of the thickness of, depths to, and lateral extents of these 

clays are also important for developing regional groundwater 

models, which are used to develop water resource management plans (for example, the Rio Grande Decision Support 

System, http://cdss.state.co.us/basins/Pages/RioGrande.aspx, 

accessed September 2014).

The National Park portion of Great Sand Dunes National 

Park and Preserve is located in east-central San Luis Valley, 

Colorado (fig. 1). The area overlies the eastern limit of the 

confining clay layers of the Alamosa Formation, but the depths 

to clay and limits of its extent are poorly known because of the 

extensive sand cover. To help address these unknowns and aid 

the National Park Service (NPS) in meeting their needs to better understand their groundwater resources, USGS geophysical efforts have focused on the National Park area. Several 

geophysical surveys were conducted over the park and vicinity, including time-domain electromagnetic (TEM) soundings 

and airborne surveys designed to image electrical resistivity 

as much as 984 ft (300 m) deep. As with electrical borehole 

logs, geophysicists use variations in electrical resistivity (or 

its inverse, electrical conductivity) in sand-clay environments 

to infer variations in sediment grain size and water quality 

with depth (Keys, 1990, 1997; Fitterman and Labson, 2005; 

Knight and Endres, 2005). Preliminary findings from the TEM 

soundings identified a strong electrical conductor that could be 

generally correlated with the presence of blue clay recorded in 

a few deep wells in the vicinity of the park (Fitterman and de 

Souza Filho, 2009; Fitterman and Grauch, 2010). A subsequent airborne TEM survey consistently detected this electrical conductor over a wider area of the park (Bedrosian and 

others, 2012; Grauch and others, 2013). Although correlations 

between the geophysical survey results and the lithologies in 

the wells appear good, the sparse and sometimes poorly documented well information does not provide a comprehensive 

test of the hypotheses.

A cored well, which collects whole samples rather than 

cuttings, provides a key to testing hypotheses developed 

from the geophysical studies and answers questions about the 

history and evolution of Lake Alamosa. Therefore, when the 

NPS began plans to drill 10 groundwater-monitoring wells 

along the western boundary of Great Sand Dunes National 

Park in 2009 (HRS Water Consultants, 2009; Harmon, 2010), 

the USGS proposed a supplemental cored well using the same 

drilling crew. A site was chosen adjacent to the NPS boundarypiezometer well BP-3, at the southwest corner of the park 

(fig. 1). The choice was guided by the results of TEM soundings collected at each of the 10 boundary-piezometer well sites 

before drilling began (D.V. Fitterman, USGS, unpub. report, 

2009). The BP-3 site offered a reasonable, predicted depth of 

235 ft (72 m) to the electrical conductor, inferred to be massive clay. This prediction turned out to be fairly accurate.

The BP-3-USGS well is located at latitude 

37°43ʹ18.06ʺN. and longitude 105°43ʹ39.30ʺW., or 435,879E., 

4,175,185N. (meters) using a Universal Transverse Mercator 

zone 13 map projection with North American Datum of 1983. 

The well was drilled through poorly consolidated sediments 

from a surface elevation of 7,549 ft (2,301 m) (NAVD 88 vertical datum) to a total depth of 326 ft (99.4 m) from September 

14 through 17, 2009. It was sited 69 ft (21 m) southwest of the 

much shallower NPS boundary-piezometer well BP-3, with 

total depth of only 79 ft (24 m).

Water began flowing from the BP-3-USGS well once 

drilling reached a depth of 141 ft (43.0 m) after penetrating 

a clay-rich layer that was first intercepted at a depth of 119 ft 

(36.3 m), elevation 7,430 ft (2,265 m). Approximately 69 ft 

(21 m) of core was recovered (about 21 percent), almost exclusively from clay-rich zones. Coarser grained fractions were 

collected as viscous fluid extruded from inside the core barrel 

or captured from upwelling drilling fluids. Wireline geophysical logs acquired include natural gamma-ray, full waveform 

sonic, density, neutron, resistivity, spontaneous potential (SP), 

and induction logs. The well is now plugged and abandoned. 

Drilling and logging of BP-3-USGS was accomplished by the 

USGS Central Region drilling unit. Funding was provided by 

the National Cooperative Geologic Mapping Program. NPS, 

as well as HRS Water Consultants, Inc., who were contracted 

to oversee the 10 other wells, provided logistical support and 

technical advice.

Due to unanticipated limitations of personnel and 

resources after drilling was completed, systematic examination 

of the well samples and additional processing of geophysical 

logs did not begin until the end of 2013. This report presents 

the results of these efforts and includes information obtained 

from a 2012 study, which was limited to an examination of 

only core samples. We present basic lithologic descriptions 

of all the well samples, information on fossil occurrence, and 

data for geophysical logs for BP-3-USGS after basic data processing. A previous report details digital signal processing of 

the full waveform sonic log (Burke, 2011). All core and other 

types of samples from the well are archived at the USGS Core 

Research Center in Denver, Colo. (see http://geology.cr.usgs.

gov/crc/).
Regional Setting and Geophysical Studies 3

Figure 1. Location of BP-3-USGS 

well, the inferred limit of the last high 

stand of Pliocene and Pleistocene Lake 

Alamosa before its disappearance (from 

Machette and others, 2013), and the 

Hansen Bluff core site near Great Sand 

Dunes National Park and Preserve in 

Alamosa County of southern Colorado.

San Luis

Lake

 Arkansas River

Rio Grande

Denver

COLORADO

Map

area

Sangre de Cristo Mountains Sangre de Cristo Mountains Sangre de Cristo Mountains Sangre de Cristo Mountains

San Juan Mountains San Juan Mountains San Juan Mountains San Juan Mountains 38°

37°

106° 105°

Hansen Bluff core

S A N

L U I S

V A L L E Y

COLORADO

NEW MEXICO

Alamosa

GREAT SAND

DUNES NATIONAL 

PRESERVE

GREAT SAND DUNES

NATIONAL PARK

BP-3-USGS

Inferred

high-stand

limit of 

Lake 

Alamosa

0 10

0 10

20 MILES

20 KILOMETERS

Regional Setting and Geophysical 

Studies

Great Sand Dunes National Park and Preserve is located 

at the eastern margin of the San Luis Valley in Colorado, 

nestled against an embayment in the Sangre de Cristo Mountains (fig. 1). The valley is underlain by thick deposits (up to 

thousands of meters) of poorly consolidated sediments that 

accumulated over the past 25–30 million years during basin 

subsidence that accompanied the formation of the Rio Grande 

rift. Rifting continues today at the Sangre de Cristo Mountains front along one of the most seismically active faults in 

Colorado (Kirkham and Rogers, 1981; Ruleman and Machette, 

2007). Great Sand Dunes National Park and Preserve is 

located over the deepest part of the Rio Grande rift basin in the 

valley, encompasses a segment of the paleoseismically active 

range-front fault, and covers the inferred eastern limit of the 

hydrologically important clays that underlie most of the San 

Luis Valley.

The Alamosa Formation is associated with Lake Alamosa, the large lake that occupied most of the San Luis 

Valley during the Pliocene and Pleistocene (Siebenthal, 

1910; Machette and others, 2013). The formation consists of 

fluvio-lacustrine sediments, including massive clay to interbedded clay and sand as much as hundreds of meters thick 

(Huntley, 1979b). The sediments accumulated within tectonically subsiding rift basins while the lake was expanding and 

contracting in response to climate changes (Brister and Gries, 

1994; Machette and others, 2013). Although lacustrine clastic 
4 Sample Descriptions and Geophysical Logs for Cored Well, Great Sand Dunes National Park, Colorado

deposits have been mapped at the surface, most of the evidence of the massive clay left behind by the lake is found in 

wells (Huntley, 1979a,b; Machette and others, 2007, 2013). 

The number and thickness of clay layers increase from west to 

east across the San Luis Valley (Huntley, 1979b). After Lake 

Alamosa disappeared, the valley was covered by fluvial and 

eolian deposits. The margins of the valley were also episodically inundated by alluvial-fan and glacial deposits (Colman 

and others, 1985; Madole and others, 2008; Madole and 

others, 2013).

Multidisciplinary investigations of measured sections 

of the Alamosa Formation and a core hole collected near 

Hansen Bluff, 24 mi (38 km) to the south of the BP-3-USGS 

(fig. 1), provide detailed information about the lithology and 

depositional environment over time (Rogers and others, 1985, 

1992). The core and surface samples comprise a sediment and 

fossil record from 2.67 to 0.67 million years ago (Ma [Megaannum]), as determined from paleomagnetic measurements 

on the samples and correlation of several ash layers to dated 

eruptions in the western United States. However, this section 

may not include the uppermost part of the Alamosa Formation, 

which should have persisted until at least 0.44 Ma (Machette 

and others, 2013). Several oil and gas wildcat wells also 

drilled through the Alamosa Formation, encountering thick 

clays, claystones, and fossil debris (Huntley, 1979b; Brister 

and Gries, 1994). Brister and Gries (1994) noted the presence 

of widely distributed, poorly cemented sandstone horizons 

near the top of the Alamosa Formation. They considered these 

horizons to mark the beginning of the demise of the lake.

Groundwater underlying San Luis Valley and Great 

Sand Dunes National Park primarily resides in two principal 

aquifers: a shallow unconfined aquifer and a deeper confined 

aquifer (Emery and others, 1973; Huntley 1979a; Hearne and 

Dewey, 1988). The shallowest impermeable clay layer within 

the Alamosa Formation (the blue clay) forms the separation 

between the two aquifers locally. The upper confining clay 

layer is generally found at depths of 40–100 ft (12.2–30.5 m) 

throughout the central part of the San Luis Valley, with 

depths >100 ft (30.5 m) toward the eastern side (Emery and 

others, 1973). 

In the vicinity of the park, the unconfined aquifer is 

mainly composed of an eolian sand sheet overlying mediumto coarse-grained piedmont alluvium, which in turn overlies 

clay, silt, and fine-grained sand of the upper part of the Alamosa Formation (HRS Water Consultants, 1999; Madole and 

others, 2013). The permeability of the unconfined aquifer can 

be high but is widely variable (Huntley, 1979a). The unconfined aquifer in the vicinity of the park is primarily recharged 

from surface flow at the Sangre de Cristo Mountains front but 

mixes with precipitated water as it flows under the dune field 

(Rupert and Plummer, 2004). Some of the water discharges at 

local creeks; the rest flows southwestward and discharges in 

closed-basin lakes, such as San Luis Lake (fig. 1).

The deeper confined aquifer is composed of the lacustrine deposits of interbedded clay, sand, and gravel within the 

Alamosa Formation. The interbedded layers are difficult to 

correlate across the basin and have heterogeneous hydraulic properties (Hearne and Dewey, 1988). The extent of the 

confined aquifer is commonly mapped using the locations of 

artesian water wells (for example, Huntley, 1979a; Machette 

and others, 2007, 2013), although some wells completed in the 

confined aquifer are nonflowing (Brendle, 2002). Recharge to 

the confined aquifer occurs at the outer limits of the confining clays near the edges of the valley and flows into the 

discharge area near San Luis Lake (fig. 1) (Emery and others, 

1973; Huntley, 1979a; Rupert and Plummer, 2004). Rupert 

and Plummer (2004) observed that the major ion chemistry 

of water from the confined aquifer in wells 7 mi (11 km) 

to the northeast of BP-3-USGS is distinct from that of the 

unconfined aquifer. They also determined that the confined 

water in one of these wells had resided in the basin for about 

30,000 years. Data are lacking to determine whether the 

unconfined and confined aquifers are regionally connected 

(Huntley, 1979a; Rupert and Plummer, 2004).

Preliminary results from ground-based TEM geophysical methods (Fitterman and de Souza Filho, 2009; Fitterman 

and Grauch, 2010; Grauch and others, 2010) showed a highly 

resistive thin layer near the surface, a strong signal from an 

electrical conductor at depths of 150–330 ft (50–100 m), and a 

transitional layer of low electrical resistivity in between. The 

electrical conductor was interpreted as a regionally persistent, 

thick clay that correlates with the blue clay in the few existing 

deep wells in the area. The top resistive layer was interpreted 

as sand cover. The transitional layer was interpreted as finegrained sediment, a combination of sand and clay, or both. 

Subsequent airborne TEM surveys confirmed these general 

observations, providing greater detail on the variations in 

depth and thickness of the three interpreted geophysical layers 

across a broad area of the park and vicinity (Bedrosian and 

others, 2012).

Drilling Operations

The drilling and geophysical logging were conducted by 

the USGS Central Region drilling unit located in Denver, Colorado, who were already on contract to NPS for the 10 wells 

they were drilling along the boundary of the park. Drilling was 

initiated on September 14, 2009, using a mud-rotary method 

for the first 60 ft (18.3 m) and coring methods thereafter. 

After coring from 60 to 80 ft (18.3 to 24.4 m) depth, 6-inch 

(in.) schedule 40 polyvinyl chloride (PVC) casing was set to 

a depth of 67 ft (20.4 m). Core sampling was attempted after 

every 10-ft (3.0-m)-depth interval, but the intervals varied 

from 2 ft (0.6 m) to 18 ft (5.5 m) to accommodate variations 

in sample recovery that depended on the quantity and distribution of clay. To acquire core samples, the 10-ft (3-m)-long core 

barrel was pulled from the well (fig. 2A). Rubber teeth within 

a metal fitting screwed to the bottom of the barrel, called a 

core catcher, are designed to let core travel up into the barrel 

but not fall out of it. After the core catcher and any sediment 
Drilling Operations 5

Figure 2. Photographs of drilling operations. A, At the end of a core run, the barrel is lifted out of the hole onto one of the several 

sawhorse setups. B, Once placed, the core catcher is unscrewed from the bottom of the barrel and any sediment removed. C, The barrel 

is moved to a different sawhorse apparatus and the core extruded by a plunger inserted into the top. Pictured, left to right, are Steve 

Grant, Mike Williams, and Derek Gongaware, U.S. Geological Survey (USGS) drilling crew. D, The core and fluids are extruded onto a 

lengthwise split of polyvinyl chloride (PVC) pipe for sampling. E, Stream of water that was flowing out of the drill stem into the mud pool 

the morning of September 17, 2009. F, Setting up for borehole logging. The tools are stored in the PVC tubes lined up along the truck 

bed. The reel for the wire is partially visible at the top right of the photo. Pictured, left to right, Barbara Corland and Steve Grant, USGS. 

Photographs by V.J.S. Grauch (A–E) and Harland Goldstein (F ).
6 Sample Descriptions and Geophysical Logs for Cored Well, Great Sand Dunes National Park, Colorado

trapped inside were removed from the end of the barrel, 

the remaining material was extruded from the barrel onto a 

lengthwise-split of PVC pipe that was lying on a saddle-horse 

apparatus (figs. 2B–2D).

Early on, it appeared that sands were flowing out of 

the core barrel and into the drilling mud, leaving very little 

material inside the barrel for sampling. Thus, the decision 

was made to pull the core barrel only for those 10-ft intervals 

where significant clay was encountered. Short intervals (<1 ft) 

of clay were sometimes all that was recovered as core. Below 

261 ft (80 m) depth, the increased proportion of clay allowed 

for better core recovery and core runs (when the core barrel 

was pulled and samples were recovered) occurred at 2- to 7-ft 

(0.6 to 2.1-m)-depth intervals. 

Bentonite mud was used during drilling below 90 ft 

(27.4 m) to keep the hole open after attempts to use water 

mixed with polymer in the interval 80 to 90 ft (24.4 to 27.4 m) 

proved unsuccessful. Groundwater began flowing out of the 

well at about 0.25 gallons per minute (gal/min) (0.016 liters 

per second [L/s]) once drilling reached 141 ft (43 m) depth. 

The flow rate had increased to 10–20 gal/min (0.631–1.26 L/s) 

by the time the drill stem was pulled for the night from 276 ft 

(84 m) depth on September 16. During the night, the artesian flow flushed out the drilling mud (fig. 2E), and the sides 

of much of the hole collapsed. The hole had to be reopened 

before coring could resume the next morning.

Coring was completed on September 17 at a depth of 

326 ft (99.4 m) when the drilling budget was expended. 

The well was then logged using six different borehole tools 

(fig. 2F). The next day, the hole was plugged with cement 

and surface casing removed. The site was cleaned up and 

abandoned. 

Procedures for Lithologic Descriptions

Lithologic descriptions of the well samples are included 

in appendix 1. The quality and accuracy of these descriptions 

are dependent on the sampling procedures, effects of subsequent storage and handling, laboratory methods employed, and 

strategies for positioning the samples relative to well depth. 

Some of these procedures proved challenging for BP-3-USGS; 

they are described in the following sections to provide context 

for the lithologic logging that was undertaken.

Sampling Procedures

Types of samples fall into one of two general categories 

depending on where the material was collected: core barrel samples or mud stream samples. Collection of material 

extruded from the core barrel was relatively straightforward. 

Other sampling strategies were required to collect sediment 

that moved out of the core barrel into the mud stream. Table 1 

summarizes the types of samples and what they represent, 

with illustrative photos shown in figures 3 and 4. More detail 

is included in the following sections.

Mud Stream Samples

For the first 60 ft (18 m) of rotary drilling, sieves were 

placed in the mud pool next to the drill rig. Material was 

removed from a sieve at specified depth intervals and collected in plastic bags. The mud stream also flowed through 

a shale shaker, or hopper, which separated the sediment into 

coarse and fine fractions. Samples from the hopper were only 

collected occasionally at the shallower depths and put in 

plastic bags.

After core runs provided little material from 70 to 101 ft 

(21.3 to 30.8 m) depth, the drillers concluded that small 

amounts of clay were clogging the core catcher and forcing 

coarser grained sediment to come up with the drilling fluid 

rather than enter the barrel. As a result, samples from the 

mud stream received greater attention, and strategies were 

developed to capture sediment from the stream. Some experimentation was required, and the strategy evolved as drilling 

proceeded.

From 101 ft (30.8 m) to 119 ft (36.3 m), samples sieved 

from the mud stream were collected every few feet because 

drilling speed indicated mostly sand. When drilling speed 

slowed significantly through tighter material (presumably 

clay) from 119 ft (36.3 m) to 131 ft (39.9 m), the core barrel 

was pulled several times and sieve samples were not collected. 

Below 131 ft (39.9 m) depth, a new sampling strategy was 

employed to try to capture greater amounts of fine-grained 

material. In this strategy, mud flowing out of the casing during 

a 10-ft (3.0-m) drilling interval was collected periodically in 

a bucket. At the end of the interval, water was added and the 

bucket allowed to sit. After a time, the fluids were decanted 

and the remaining sediment collected in a plastic bag. Thus, 

bucket samples represent an amalgamation of sediment over 

an interval. With greater clay content in the lower depths 

of the well, very little material was obtained from bucket 

samples, especially in comparison to the volume recovered as 

core. Combined with observations that the lithologies of these 

later bucket samples were all very similar, we conclude that 

these bucket samples mostly represent sediment that was circulated by the drilling fluid from shallower parts of the well.

Core Barrel Samples

Material extruded from the core barrel included intact 

core or core pieces, viscous fluid (sediment slurry or water 

with suspended sediment or mud), and clay-rich sediments 

caught in the core catcher at the bottom of the barrel. Commonly, clay core became stuck in the barrel requiring extrusion using a power air hose. Two times the extrusion proved 

explosive and core ended up on the ground. One time, clay 

was stuck in the barrel and ended up attached to the subsequent core run. These incidents are noted in the lithologic 

descriptions (appendix 1). 

The core catcher and the sediment within it were removed 

before material was extruded from the barrel. Sediment was 

removed from the core catcher with a scoop and placed in a 
Procedures for Lithologic Descriptions 7

Table 1. Explanation of and procedures for different sample types.

[PVC, polyvinyl chloride]

Sample type Explanation and procedures Illustrative figure

Mud stream samples

Sieved cuttings Mud streaming out of the well and collecting in a sieve with medium-sized (1/16 inch) mesh. 

The sieve was pulled from the mud pool and sampled when drilling reached a specified 

depth. These types of samples were only collected for the top 60 ft (18.3 m) of depth, before 

coring commenced. 

Figure 3A

Sieve sample Mud streaming out of the well after passing through a sieve with medium-sized (1/16 inch) 

mesh. Samples collected when drilling reached a specified depth. These types of samples 

were collected only after coring had commenced.

Figure 3B

Hopper sample (coarse 

and fine fractions)

Samples collected from the mud stream after it was separated into coarse and fine fractions by 

a shale shaker (hopper). 

Bucket sample Sediment collected as follows: Samples of mud flowing out of the well were periodically 

amassed into a bucket over a specified depth interval. After adding water, the bucket was 

left sitting in order for sediment to naturally separate from the fluid. The fluid was then 

decanted from the bucket and the remaining sediment collected.

Figures 3C, 3D

Hand sample Hand selected specimens collected from a sieve sample or from the hopper.

Core barrel samples

Core Intact core or core segments that remained contiguous with one another in their original orientation as they were extruded into the lengthwise split of PVC pipe. 

Figure 4A

Viscous fluid sample, 

scooped

Sample of water with suspended sediment or mud that flowed from the core barrel. Highviscosity samples were scooped directly into a plastic bag.

Figure 4B

Viscous fluid sample, 

sieved

Sample of water with suspended sediment or mud that flowed from the core barrel. Lowviscosity fluids were sieved before collecting in a plastic bag.

Figure 4C

Core catcher sample Sample of sediment caught inside the core catcher, a metal fitting at the bottom of the core 

barrel. Only clay-rich sediments were trapped by the core catcher, so thin clay beds within 

sandy intervals were sampled preferentially. 

Figure 4D

Core piece A short piece of intact core placed in a bag rather than in PVC pipe.

plastic bag, which was labeled with the core-run number and 

depth interval.

Intact core was extruded from the core barrel into a 10-ft 

(3.0-m)-long split of PVC pipe. It was measured, photographed, then transferred to another lengthwise split of PVC 

pipe that was 5 ft (1.5 m) long or shorter to match the length 

of the core. The 5-ft (1.5-m) maximum was chosen to facilitate core storage and handling. Most of the core was washed 

before it was wrapped in plastic, and the top split of the 

shorter PVC pipe placed on top. Any extra space within the 

pipe at the ends of the core was filled with floral foam before 

the two PVC halves were secured together with tape. The 

PVC and plastic wrap were labeled using the core-run number, 

depth interval, and an arrow indicating which end of the core 

is up (shallowest).

In a few cases (noted in appendix 1), intact core was 

divided into pieces. The reasons include (1) forcible extrusion 

ended with some of the core on the ground, so the original 

orientation was uncertain; (2) part of the core was deformed, 

so it was cut off and bagged; and (3) the core exceeded the 5-ft 

length of the PVC pipe used for storage, so that the core was 

divided.

Where viscous fluid was extruded instead of consolidated 

sediment, samples were collected using a scoop or by pouring 

the fluid through a sieve into a plastic bag (table 1; noted in 

appendix 1). The bags were labeled with the core-run number 

and depth interval.
8 Sample Descriptions and Geophysical Logs for Cored Well, Great Sand Dunes National Park, Colorado

Figure 3. Photographs of various sampling procedures for mud stream samples. A, A cuttings sample is sieved and collected from 

the pool of mud next to the drill stem during the first 60 feet of rotary drilling. B, A sieve sample is collected from the mud stream while 

coring. The sieve, attached to a long handle, collects mud that is streaming up the sides of the core barrel and out of the hole. C, Mud 

streaming from the hole is collected periodically in a small bucket and emptied into a large bucket during the collection of a bucket 

sample. Pictured, left to right, Steve Grant and Jeff Eman, U.S. Geological Survey (USGS). D, At the end of the drilling interval, fluid from 

the large bucket is decanted and the remaining sediment stored as the bucket sample. Pictured, left to right, Jeff Eman and Harland 

Goldstein, USGS. Photographs by V.J.S. Grauch.
Procedures for Lithologic Descriptions 9

Figure 4. Photographs of various sampling procedures for core barrel samples. A, Intact core after extrusion onto a split half of 

polyvinyl chloride (PVC) pipe on a sawhorse apparatus. B, Viscous fluid collected with a shovel from poorly consolidated core that 

was extruded along with intact core (not shown). C, Viscous fluid poured through a sieve from the core barrel and collected as a 

sieved sample. D, Example of a core catcher sample before it was bagged. After detaching the core catcher at the bottom of the core 

barrel, sediment is inside the fixture and extending outside. Most other core catcher samples did not extend this far outside the fixture. 

Photographs by V.J.S. Grauch.
10 Sample Descriptions and Geophysical Logs for Cored Well, Great Sand Dunes National Park, Colorado

Effects of Storage and Handling

During the more than 4 years that samples were stored 

before examination, most of them dried out. Much of the clay 

making up the core samples contracted and broke into smaller 

pieces. Thus, the core was never split, fearing that such 

attempts would further disintegrate the samples. The bagged 

samples fared better; some of these retained a little of the 

original fluid that had been captured along with the sediment. 

Additional problems for the clay-rich samples were changes in 

color and biologic growth observed since acquisition, suggesting that chemical reactions had taken place. As a result, 

accurate color descriptions and chemical sampling were not 

attempted.

The desiccation and disaggregation of the clay-rich core 

samples affected measurements of core length between collection and examination. Shrinkage was most notable for the 

core samples containing the most clay, at depths below 261 ft 

(79.6 m). On the other hand, disaggregation of the desiccated core also resulted in expansion of total length because 

the pieces tended to separate and leave cracks between them. 

This problem is exacerbated by repeated handling of the core. 

Table 2 lists measured core lengths at original acquisition 

compared to two subsequent episodes of examination showing 

where core length has varied.

Photographs that capture how samples appeared at the 

drill site may be downloaded from the Photos folder, which 

also includes an index file describing the contents of the 

photographs. These photos are the best record of the conditions of the samples at the time they were collected, especially 

regarding color and sedimentary structures. Figure 5 shows 

an example of a clay-rich piece of core as it looked at the time 

of its collection compared to its appearance after more than 

4 years of storage. Note the change in color and obscuring of 

oval blotches of different color that may be part of an important biogenic or sedimentary feature. Figure 6 demonstrates 

how the subtle color differences between samples from blue 

versus gray clay are obvious right after collection, but not so 

after they dried out. 

Table 2. Core lengths recovered onsite in 2009 and changes in measured lengths in years 2012 and 2013.

[cm, centimeter; --, no data; %, percent]

Core run*

Drilling depth 

interval, 

in feet

Core length 

recovered in 2009, 

in inches (cm)

2012 measured 

length, 

in inches (cm)

2013 measured 

length, 

in inches (cm)

2012 change 

from 2009

2013 change 

from 2009

9 125–128 12.0 (30.5) -- 12.0 (30.5) -- 0.0 %

11 131–141 7.5 (19.1) 7.9 (20.0) 10.0 (25.4) +5.0 % +33 %

13 171–191 47.0 (119.4) 47.2 (120.0) 48.0 (121.9) +0.5 % +2.1 %

14 191–201 38.0 (96.5) 35.4 (90.0) 37.0 (94.0) –6.8 % –2.6 %

15 210–211 20.0 (50.8) 20.1 (51.0) 20.0 (50.8) +0.4 % 0.0 %

16 211–221 26. 0 (66.0) 24.8 (63.0) 26.0 (66.0) –4.6 % 0.0 %

17 (top) 231–241 57.5 (146.1) 55.9 (142.0) 57.5 (146.1) –2.8 % 0.0 %

17 (bottom) 231–241 29.8 (75.6) 28.3 (72.0) 29.4 (74.7) –4.7 % –1.2 %

18 (top) 251–261 57.5 (146.1) 51.6 (131.0) 57.5 (146.1) –10 % 0.0 %

18 (bottom) 251–261 17.0 (43.2) 13.8 (35.0) 17.0 (43.2) –19 % 0.0 %

19 261–266 54.0 (137.2) 45.7 (116.0) 48.0 (121.9) –15 % –11 %

20 266–271 45.5 (115.6) 39.4 (100.0) 42.0 (106.7) –13 % –7.7 %

21 271–276 44.0 (111.8) 35.4 (90.0) 38.0 (96.5) –20 % –14 %

22 276–291 11.0 (27.9) 9.1 (23.0) 10.0 (25.4) –18 % –9.1 %

23 291–301 59.0 (149.9) 57.9 (147.0) 60.0 (152.4) –1.9 % +1.7 %

24 301–306 60.0 (152.4) 56.3 (143.0) 60.0 (152.4) –6.2 % 0.0 %

25 306–311 24.0 (61.0) 22.8 (58.0) 23.0 (58.4) –4.9 % –4.2 %

26 311–316 57.0 (144.8) 54.3 (138.0) 54.0 (137.2) –4.7 % –5.3 %

27 316–321 60.0 (152.4) 53.2 (135.0) 54.0 (137.2) –11 % –10 %

28 321–326 55.0 (139.7) 49.6 (126.0) 52.0 (132.1) –9.8 % –5.5 %

*Core was not recovered from all core runs. Cores recovered from runs 17 and 18 were divided into top and bottom pieces on site and stored separately.
Procedures for Lithologic Descriptions 11

Figure 5. Photographs of a selected core at time of collection compared to more than 4 years 

later. A, Washed core piece from the bottom of core run 25 (depths 306–311 ft) on September 17, 

2009. Note the dark oval splotch that may be a sedimentary structure or trace fossil. B, The same 

core piece as it looked on February 5, 2014, after it had been wrapped in plastic and stored inside a 

polyvinyl chloride (PVC) pipe. Note the color change, breakage, and difficulty seeing the oval splotch. 

Photographs by V.J.S. Grauch (A) and Gary L. Skipp (B).
12 Sample Descriptions and Geophysical Logs for Cored Well, Great Sand Dunes National Park, Colorado

Figure 6. Photographs of two clay samples of differing color at time of collection in September 2009 compared to almost 5 years later 

in August 2014. A, Clay with blue tint at time of collection as a core catcher sample at 266 ft depth (core run 19). B, Clay with even-gray 

color at time of collection from ≈311 ft depth (core run 26). C, Clay from the same sample as in A after almost 5 years of storage in a 

plastic bag. Note the color change. D, Clay from the same core sample as in B after almost 5 years of storage wrapped in plastic in a 

polyvinyl chloride (PVC) pipe. Note the extensive disaggregation and the color change for a small piece of the core on the right-hand 

side of the photo. Photographs by V.J.S. Grauch (A and B) and Gary L. Skipp (C and D).
Procedures for Lithologic Descriptions 13

Laboratory Methods

All samples from the well were examined and described 

regarding grain sizes, types, and shapes; sorting, layering, and 

sedimentary structures; calcium carbonate content; occurrence 

of fossils or other biogenic material; evidence of biologic 

activity such as trace fossils or bioturbation; and presence 

of volcanic ash (appendix 1). Some samples were examined 

for mineralogy using X-ray diffraction analysis. Difficulties 

in sample recovery and the effects caused by the long period 

of sample storage affect how well these descriptions actually 

represent the lithology at depth. Specific depths that were 

sampled are uncertain for core samples that are shorter in 

length than the drilling depth interval. 

Bagged samples from the drilling and coring were first 

identified as to type of sample (table 1). Cores were first wetted with a spray bottle then scraped to a depth of several millimeters on a portion of the core over the entire length. Scraping 

was done to remove core barrel smear contamination. Wetting 

was done for visual enhancement of any structures present 

(bedding, laminations, faulting, bioturbation, contacts, grain 

size changes, and so forth). Because some of the core had 

fragmented, a representative piece within broken intervals was 

chosen for wetting and scraping.

Both bagged and core samples were then examined under 

a binocular microscope to observe grain size and shape, sorting, grain color, and some mineralogy. The relative quantity 

of calcium carbonate (calcareous degree) was estimated from 

the intensity of effervescence after application of a 10-percent 

solution of hydrochloric acid (HCl). Core samples were tested 

every few inches. Samples suspected to contain fossils or 

unusual mineral assemblages were viewed under the binocular microscope. Some such samples were tested for magnetic 

grains using a magnet. Several samples were chosen for X-ray 

diffraction analysis to determine mineralogy. A subset of 

these samples were mounted (smear slide) for petrographic 

examination.

Occurrences of animal remains and evidence of biologic activity were noted during the systematic examination 

of bagged and core samples in 2013 by G.L. Skipp and by 

M.E. Benson and J.K. Davis while studying core samples in 

2012. Most fossil specimens were categorized as bivalves, 

gastropods, ostracods, or unidentified shells. A few samples 

were examined by M.E. Benson for the potential presence of 

diatoms. Where diatoms were found, they were preliminarily 

identified. Bones and teeth were distinguished, where possible, 

but no effort was made to identify the animal type, as remains 

were not intact. Other evidence of animal or plant life included 

fine organic debris, woody plant parts, or bioturbation, none of 

which was researched in detail. Appendix 2 provides descriptions of the fossils or other evidence of life and the depth 

intervals where they were observed. Because core length 

measurements differed between the 2012 and 2013 studies, 

the locations of the occurrences within the core samples are 

listed separately and should be considered approximate for 

future work.

Samples taken for X-ray diffraction analysis were ground 

to <200 mesh size (≈10 micrometer [μm]) and packed into a 

cavity mount. Analysis was performed on a Philips R150 goniometer with a XRG3100 generator using a 2°-theta scan range 

of 6–65. Resulting X-ray diffraction patterns were evaluated 

for characteristic patterns of common minerals. The resulting 

bulk mineralogy for each sample is listed in appendix 3.

Sample Descriptions Versus Well Depths

Findings from the sample descriptions detailed in appendix 1 are depicted graphically versus well depth in figure 7, 

divided in two columns by sample type. Assigning the findings 

to specific depths within the well is not straightforward due 

to uncertainties caused by poor core recovery and difficulties 

in sampling sands. The uncertainties, and thus how depths 

were estimated, are different for mud stream versus core barrel samples. For mud stream samples collected over specific 

depth intervals, uncertainties arose as to whether they accurately represent the sediment in the well over that interval. For 

core samples that were shorter than their associated drilling 

interval, uncertainties arose regarding their positions within 

that interval.

Mud stream samples collected during the first 60 ft of 

rotary drilling (sieved cuttings and hopper samples) were 

obtained as cuttings of all sediment and are considered to 

adequately represent the intervals they sampled. Below this 

depth, sieve and bucket samples were also collected for specified depth intervals, but the sediment may not adequately 

represent the sediment within that depth interval because of 

possibilities of mixing with sediment from uphole depths. On 

the other hand, the volume retrieved in bucket samples significantly decreased as more clay was recovered as core. This 

correlation, along with very similar lithology noted for these 

minimal-volume samples, suggests that the quantity of contaminating material was limited. In any case, bucket samples 

with minimal volume are not reliable samples, because they 

may not be representative of the depth interval sampled, and 

are noted with question marks on figure 7.

Depth placement of most core samples was evaluated 

using matches of the lithology of the sample to the description 

of sediment encountered in the interval onsite and supporting evidence from the geophysical logs. Some matches relied 

primarily on the geophysical logs. Depth intervals of core 

could also be estimated relative to the underlying core catcher 

sample. Depths were generally easier to estimate for core 

catcher samples because they commonly represented the last 

clay recognized by drilling speed before the driller pulled the 

core barrel. In all but one case, core that was extruded from 

the barrel in pieces could be considered contiguous. The one 

exception is core run 13 (depth interval 171–191 ft), where 

core was extruded as many pieces (4-ft total length) along with 

viscous fluid (appendix 1 and fig. 7). If the many pieces were 

considered contiguous, the clay and cemented sand layers 

observed did not match in depth compared with relative lowversus high-resistivity values in the geophysical logs. The 

matches were improved if a gap in core recovery was inferred.
14 Sample Descriptions and Geophysical Logs for Cored Well, Great Sand Dunes National Park, Colorado

Figure 7. Graphical summary of lithologic descriptions and other observations versus inferred well depth. More detail and explanatory 

material can be found in appendixes 1 and 2. Because knowing the sample type is important for understanding the significance of the 

observations and for inferring depth ranges of the samples, two columns divided by sample type are shown side by side. The positions 

of the codes for notable features only approximately depict where they are positioned relative to core samples.

Calcareous

degree

Calcareous

degree

Grain size Grain size

Mud stream samples Core barrel samples

NoneHighNoneHigh

claysiltvery fine sandfine sandmedium sandcoarse sandclaysiltvery fine sandfine sandmedium sandcoarse sand

Rotary 

drilling

Core run 1

Core run 2

Core run 4

Core run 5

Core run 6

Core run 7

Core run 8

Core run 9

Core run 10

Core run 11

Core run 12

Core run 3

No sample

No sample

No sample

Drilling

notes

?

Sieved cuttings and hopper samples

Sieve sample

Bucket sample—Dashed where recovery 

was minimal; part or all of the material 

may have come from other depths

EXPLANATION

Mud stream sample types

Viscous fluid sample—Dashed where 

representative interval is indeterminate

Core catcher sample or core piece—

Dashed where depth is indeterminate

Core sample—Dashed where depth is 

indeterminate

Core barrel sample types

Maximum depth limits

Grain size—Boxes placed within the 

labeled grain-size fraction lines 

indicate grain sizes observed. 

Samples that may not be representative are queried

Calcareous degree—Bar-graph boxes 

indicate calcareous degree observed, 

increasing to the right

Lithologic indicators

Mixed viscous fluid and core catcher 

samples—Dashed where the representative interval is indeterminate

Sample typeSample type

a—Glass shards—probably associated with 

volcanic ash

bn—Bones of unknown type

bu—Burrows

bv—Bivalves

g—Gastropods

o—Ostracods

p—Woody plant part

f—Fish bones

or—Organic matter

sh—Shells or shell fragments

st—Sedimentary structure

u—Unknown circular white grains

v—Vertebrate tooth or bone

x—Sample collected for X-ray diffraction analysis

rt—Root traces

d—Diatoms

Notable 

features

Notable 

features

Mud stream sample depth limits—

Maximum depth limits bounding the 

interval that mud stream samples 

represent

Core barrel sample depth limits—Maximum 

depth limits within which core barrel 

samples can be reasonably positioned

Notable features

d, x

bi?

x

x

x

No sample

No sample

No sample

0

20

40Depth, in meters

0

50

150

100Depth, in feet

bi—Bioturbation
Procedures for Lithologic Descriptions 15

Figure 7. Graphical summary of lithologic descriptions and other observations versus inferred well depth. More detail and explanatory 

material can be found in appendixes 1 and 2. Because knowing the sample type is important for understanding the significance of the 

observations and for inferring depth ranges of the samples, two columns divided by sample type are shown side by side. The positions 

of the codes for notable features only approximately depict where they are positioned relative to core samples.—Continued None High

Calcareous

degree

NoneHigh

Grain size Calcareous

degree

Grain size

Mud stream samples Core barrel samples clay silt very fine sand fine sand medium sand coarse sand clay silt very fine sand fine sand medium sand coarse sand

Core run 13

Core run 14

Core run 15

Core run 16

Core run 17

Core run 18

Core run 19

Core run 20

Core run 21

Core run 22

Core run 23

Core run 24

Core run 25

Core run 26

Core run 27

Core run 28

Drilling

notes

?

?

?

?

?

?

?

?

?

?

?

?

?

?

?

?

missing

core?

Sample typeSample type

Notable 

features

Notable 

features

o

bv

o

a

sh

a, sh

a, o

a

o

og, o

a, bv

bv, o, sh

bv, f?

sh

o, u

g, o, sh, u

bi, g, or, p, u, v

bi?, sh, x

bi, bu, g

bu, o

bu, sh

bu, o

o, rt, u

o

d, o

o

o

o

o

o

o

o

o, x

o

o

o, x

o, sh, st

g, sh

bi, bu, g, sh

bi, bu, g, rt, sh

bn?, o

st

bv, g, o

bu, sh

x

x

x

bi, rt, x

or?, x

x

Samples

disregarded

No sample

No sample

No sample

60

80

100 Depth, in meters

200

250

300Depth, in feet

Sieved cuttings and hopper samples

Sieve sample

Bucket sample—Dashed where recovery 

was minimal; part or all of the material 

may have come from other depths

EXPLANATION

Mud stream sample types

Viscous fluid sample—Dashed where 

representative interval is indeterminate

Core catcher sample or core piece—

Dashed where depth is indeterminate

Core sample—Dashed where depth is 

indeterminate

Core barrel sample types

Maximum depth limits

Grain size—Boxes placed within the 

labeled grain-size fraction lines 

indicate grain sizes observed. 

Samples that may not be representative are queried

Calcareous degree—Bar-graph boxes 

indicate calcareous degree observed, 

increasing to the right

Lithologic indicators

Mixed viscous fluid and core catcher 

samples—Dashed where the representative interval is indeterminate

a—Glass shards—probably associated with 

volcanic ash

bn—Bones of unknown type

bu—Burrows

bv—Bivalves

g—Gastropods

o—Ostracods

p—Woody plant part

f—Fish bones

or—Organic matter

sh—Shells or shell fragments

st—Sedimentary structure

u—Unknown circular white grains

v—Vertebrate tooth or bone

x—Sample collected for X-ray diffraction analysis

rt—Root traces

d—Diatoms

Mud stream sample depth limits—

Maximum depth limits bounding the 

interval that mud stream samples 

represent

Core barrel sample depth limits—Maximum 

depth limits within which core barrel 

samples can be reasonably positioned

Notable features

bi—Bioturbation
16 Sample Descriptions and Geophysical Logs for Cored Well, Great Sand Dunes National Park, Colorado

Most depth estimates have fair confidence. Those with 

uncertainties are indicated by dashed outlines on figure 7. In 

all cases, maximum errors on the position of the core samples 

are defined by the upper and lower limits of the drilling depth 

interval (red lines on fig. 7). Uncertainties for three core runs 

are particularly large, for which the maximum errors apply 

(runs 3, 13, and 14; fig. 7).

The depths that viscous fluid samples represent are all 

uncertain, so all outlines for these sample types are dashed 

on figure 7. Although the fluid must have sampled the depth 

interval indicated, it is likely that the entire volume of that 

interval is not adequately represented. In some cases, the 

relation of the viscous fluid to more solid portions of the core 

barrel sample was obvious after extrusion from the barrel, so 

the depth uncertainties are somewhat less.

Geophysical Logs

Six wireline geophysical tools were used to obtain logs 

of natural gamma-ray, electrical resistivity and conductivity, 

spontaneous potential, full waveform sonic, density, and neutron data and several other borehole parameters. These logs 

were chosen to augment lithologic interpretations of the well 

and to investigate physical properties of the subsurface that 

can be correlated to surface geophysical measurements and to 

other wells in the region.

Logs Acquired

Table 3 lists the tools and associated logs in the order 

they were obtained. Each tool was lowered as close as possible 

to the bottom of the hole, then data were collected at 0.1-ft 

(3-centimeter [cm]) intervals as the tool was raised.

Table 4 presents the simplified responses for the logs and 

their corresponding inferred physical parameters, modified 

from Keys (1990, 1997). Also noted in table 4 are the types of 

responses important for interpreting lithology from the logs 

measured in BP-3-USGS. Readers are referred to Keys (1990, 

1997) for additional information on interpreting the logs for 

other parameters, such as water quality and porosity.

Data Processing

Measurements originally recorded at specific times 

by each geophysical tool as it was raised by winding up its 

attached wire were converted to depth measurements using 

the number of rotations of the wire reel and industry-supplied 

coefficient values. (The reel is partially shown in fig. 2F). The 

depth measurements were then interpolated as a sequence of 

evenly spaced data points, generally using a depth spacing of 

0.1 ft (≈3 cm). The resulting sequences of data points, representing measurements every 0.1 ft (≈3 cm) down the hole, can 

then be manipulated using standard borehole and geophysical 

processing techniques. After basic processing by the logging 

Table 3. Geophysical tools and associated data logs acquired for BP-3-USGS, listed in the order they were acquired.

Tool type Tool model* Logs acquired Comments on data collected

Gamma-caliper Century Geophysical 9074 Three-arm caliper, natural gamma-ray Caliper and gamma-ray sensor were not 

calibrated.

Multiparameter Century Geophysical 8044 Natural gamma-ray, fluid resistivity, 

spontaneous potential, temperature and 

change in temperature, 16-in. and 64-in. 

normal resistivity, single-point resistance, lateral resistivity

Fluid temperature values do not appear 

valid. Tool likely was stuck at 296 ft 

(90.2 m) depth despite readings indicating greater depth. Resistivity and spontaneous potential data are noisy. Sensors 

were not recently calibrated to expected 

borehole parameters.

Induction Century Geophysical 9511 Natural gamma-ray, conductivity, resistivity (computed from conductivity)Sensors were not calibrated. Tool was not 

calibrated to downhole temperature. 

Sonic Century Geophysical 9320 Natural gamma-ray, full waveform 

acoustic properties (see Burke, 2011, for 

details)

Operators could not get the tool past a 

tight spot at 296 ft (90.2 m) depth, so 

readings were only acquired above 

this depth. Gamma-ray sensor was not 

calibrated.

Neutron Mount Sopris 2NUA-1000 Neutron Data are somewhat noisy.

Density Century Geophysical 9139 Single-arm caliper, natural gamma-ray, 

bulk density using short and long spacing, compensated bulk density

Caliper and sensors were not recently calibrated to expected borehole parameters.

*Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
Geophysical Logs 17

Table 4. Description of geophysical logs and their utility for BP-3-USGS.

[PVC, polyvinyl chloride]

Log type Parameters measured Physical parameters 

inferred

Notes important for lithologic interpretation of 

BP-3-USGS

Caliper Hole diameter Wash-outs or restrictions of the sides of 

the hole

Integrity of the well bore gives clues regarding sand 

versus clay intervals. Geophysical measurements in 

wash-outs may be affected and not representative of 

the formation. 

Natural gamma Natural-gamma radiation Clay or feldspar 

content

Radiation increases with increasing clay or increasing 

potassium associated with abundance of feldspar, such 

as in volcanic sands. Readings are attenuated inside 

PVC casing.

Normal resistivity Electrical resistivity of 

formation plus pore 

and borehole fluids, 

measured over sensor 

spacings of 16 in. and 

64 in.

Lithology, bed boundaries, and water 

quality

Resistivity generally decreases with increasing clay 

content. The 64-in. (long-normal) sensor samples 

greater volume of material vertically and laterally 

into the formation than does the 16-in. (short-normal) 

sensor, resulting in a 64-in. normal curve that is much 

smoother than the 16-in. normal curve. Readings are 

affected by borehole fluid and are not valid inside the 

PVC casing.

Induction Conductivity induced 

from electromagnetic 

fields

Lithology and bed 

boundaries

Resistivity curves computed as the inverse of conductivity data are complimentary to the normal resistivity 

curves and provide similar information. Readings are 

unaffected by PVC casing and are more impervious to 

borehole effects than the normal resistivity sensors.

Spontaneous potential Natural electrical potentialsLithology, bed boundaries, and water 

quality

Curve inflections correspond to contacts between beds of 

different lithology. Readings are not valid inside PVC 

casing.

Sonic Travel time of an acoustic wave between 

transmitters and 

receivers

Sonic velocity and 

porosity

The sonic tool was chosen for BP-3-USGS to get a 

general sense of the overall sonic velocity of poorly 

consolidated sediments in this region. The readings are 

attenuated inside PVC casing.

Neutron Neutrons slowed and 

scattered by hydrogen

Saturated porosity Increasing counts correspond to increasing volume of 

fluid-filled pore spaces. Porosity and pore connectivity 

commonly reflect differences in lithology. Clays may 

have higher porosity than sands, but the pores are not 

connected, so the effective porosity is low. The readings are attenuated inside PVC casing.

Density Scattered and attenuated 

gamma photons

Bulk density and 

porosity

The density tool was chosen for BP-3-USGS to get a 

general sense of the overall bulk density of poorly 

consolidated sediments in this region. The readings are 

attenuated inside PVC casing.

operator, we additionally checked the data for depth calibration, applied routines to eliminate spurious data and attenuate 

noise, adjusted for tool calibration problems, and corrected 

for effects of borehole fluid and hole diameter. These steps 

are described in the following sections. Description of the 

more extensive data processing of the sonic log is described 

in Burke (2011). Table 5 summarizes the types of processing 

applied for each log.

Common to the data processing of many of the geophysical logs was the application of spike-rejection and low-pass 

filters, as implemented by Geosoft OASIS for a sequence of 

evenly spaced data points. Data spikes were removed using 

a nonlinear filter, based on a procedure described by Naudy 

and Dreyer (1968). The filter rejects data points that exceed 

a particular amplitude tolerance over a certain specified 

depth interval and replaces them with an estimate based on 
18 Sample Descriptions and Geophysical Logs for Cored Well, Great Sand Dunes National Park, Colorado

Table 5. Overview of data processing steps applied to geophysical logs.

[PVC, polyvinyl chloride]

Log type Data editing Filters applied Corrections applied

Three-arm caliper None None Shifted to match expected readings inside 

PVC casing, which has fixed diameter.

Natural gamma

(five different tools)

None Low-pass None.

Normal resistivity Remove data measured within PVC 

casing and depths at bottom, below 

where the tool was stuck

Spike-rejection and 

low-pass

Corrected for borehole effects.

Resistivity from induction None Low-pass Scaled to 16-in. normal resistivity curve.

Spontaneous potential Remove data measured within PVC 

casing

Spike-rejection and 

low-pass

None.

Sonic None See Burke (2011) See Burke (2011).

Neutron None Spike-rejection and 

low-pass 

Rescale depth to match other tools.

Density None Low-pass Calibration correction.

surrounding data points. We chose amplitude tolerances of 

about 1.33 percent of the total range of data values and used 

a depth interval that spans three data points, or an interval of 

0.3 ft (9 cm). Low-pass filters were applied to smooth the data, 

using a convolution filter as described by Fraser and others 

(1966). The low-pass filter is designed to remove all features 

of the log trace that have wavelengths less than a designated 

cutoff wavelength. The filter is tapered using a taper length 

equal to the wavelength cutoff distance so that side effects of 

the filtering are minimized. For the BP-3-USGS geophysical 

logs, we used a wavelength cutoff that spans 20 data points, or 

a depth interval of 2 ft (0.61 m), except for the normal resistivity logs where a wavelength cutoff spanning 10 points, or a 

depth interval of 1 ft (0.30 m), was applied.

Check of Depth Calibration

Although natural gamma-ray logs are commonly used 

to distinguish different lithologies, comparing gamma-ray 

logs from multiple runs can also help evaluate calibration of 

depth between logs. Although the amplitudes and details of the 

gamma-ray curves in counts per second (cps) are expected to 

vary for each run of the different tools, general features should 

line up if depth is calibrated correctly. Figure 8 compares the 

three-arm caliper log and low-pass-filtered, natural gammaray logs from five different tools. The caliper records the 

diameter of the hole through which the tool passed to identify 

tight spots and wash-outs. Two wash-outs apparent from the 

wide excursions of the caliper measurements at 80 ft (24.4 m) 

and 130 ft (39.6 m) are accompanied by abrupt drops in all 

the gamma-ray curves. Although the wash-outs indicate the 

geophysical tools were not correctly measuring parameters of 

the lithology, the drop-outs in the gamma readings are well 

aligned, indicating that the depth scales on these logs are well 

calibrated. 

The overall shapes of the gamma-ray curves are well 

matched throughout most of the length of the well confirming that depth is well calibrated between logs. One exception 

comes from comparing the curves for depths below the tight 

spot at 296 ft (90.2 m) where the caliper reading reaches less 

than 4 in. (10 cm). Operators had difficulties getting most of 

the tools below this point; they abandoned attempts for the 

sonic tool. However, the multiparameter tool may not have 

reached the bottom of the hole as well, as evident below this 

point from a moderate decrease in tension (downloads directory), a lack of character in the multiparameter gamma-ray 

curve, and flat-lined resistivity readings (not shown). These 

observations suggest that the multiparameter tool was stuck at 

this tight spot. Therefore, data were eliminated from the logs 

appropriate to where each of the sensors was located on the 

probe when it reached 296 ft (90.2 m). 

Because the neutron tool did not include a natural 

gamma-ray detector, the neutron log was compared to the 

induction and SP logs to check depth calibration (fig. 9). After 

application of spike-rejection and low-pass filters to all three 

logs, many individual features of these curves were similar or 

mirror images of each other and thus should occur at the same 

depth. Instead, characteristic features of the neutron curve, 

indicated at several places on figure 9 by the dashed lines that 

cross all three logs, appear to be shifted in depth. Because the 

neutron tool was the only model produced by Mount Sopris 

rather than Century Geophysical (table 3), the depth offset of 

the neutron curve may be due to differences in the coefficient 
Geophysical Logs 19

Figure 8. Borehole diameter measured by the three-arm caliper and low-pass-filtered, natural gamma-ray curves from five 

different tools. Note that the curves are stacked using a relative scale; their absolute values are floating.

4

2 5 1 3

100 200

Counts per second

Caliper

Hole diameter, inches

Depth, in feet

EXPLANATION

Filtered gamma reading

Gamma-caliper tool

Induction tool

Sonic tool

Multiparameter tool

Density tool

Base of polyvinyl chloride 

(PVC) casing

Depth, in meters

0.0 10.0 20.0

5

3

2

1

4 10

20

30

50

70

90

0

50

150

200

250

300

100

0

50

150

200

250

300

100

0

40

60

80

100

10

20

30

50

70

90

0

40

60

80

100

PVC casing
20 Sample Descriptions and Geophysical Logs for Cored Well, Great Sand Dunes National Park, Colorado

Figure 9. Comparison of original neutron curve to induction and spontaneous potential (SP) logs to correct the depth scale for the 

neutron log. Characteristic features in the latter two logs were correlated to mirror-image features in the neutron log (correlation across 

the dashed lines) to determine how depths needed to be scaled. After depth scaling, the characteristic features align much better.

EXPLANATION

100 1,000

Original neutron log

500 1,000 1,500

Counts per second

0

50

150

200

250

300

100

-50 0

Depth, in feet

0

20

40

60

80

100

Depth, in meters

Line comparing features between logs

Neutron log after data processing

Conductivity from induction tool

Spontaneous potential from multiparameter tool after data processing

Base of polyvinyl chloride (PVC) casing

Conductivity

Millimhos per meter

Neutron

Spontaneous

potential

Millivolts

10

30

50

70

90

PVC casing
Geophysical Logs 21

values used by the two companies to determine depth from the 

number of rotations of the wire reel. A scaling factor of 0.992, 

determined by inspection, was multiplied to the depth values 

of the neutron log to fix the problem. The neutron curves 

before (orange line) and after (red line) correcting the depth 

scale are shown on figure 9.

Normal Resistivity Logs

Normal resistivity logs need to be corrected for borehole 

effects to obtain more representative measurements of the 

resistivity of the formation. Borehole effects include the resistivity of the drilling fluid, borehole diameter, volume of fluid 

invasion, and bed thickness (Keys, 1990, 1997). Scott (1978) 

presented a practical algorithm for correcting normal resistivity log data for borehole diameter and mud resistivity. The 

algorithm is derived from resistivity departure-curve charts 

developed earlier by Schlumberger Well Surveying Corporation, assuming no invasion of drilling mud and an infinite bed 

thickness. The validity of these assumptions is difficult to 

ascertain for BP-3-USGS, but they likely are not met. The correction was applied anyway, assuming it improves the results 

more than no correction at all.

Figure 10 shows the normal resistivity curves before and 

after correction and filtering. The correction used equation 2 of 

Scott (1978), incorporating a tool diameter of 2.1 in. (5.3 cm) 

and fluid resistivity values taken from those measured during 

the logging. Resistivities of the fluid varied little throughout the hole, ranging from 5.9 to 6.2 ohm-meter (ohm-m). 

The fluid was probably well distributed throughout the hole 

because of the artesian flow. Spike-rejection and low-pass filters were then applied to the corrected normal resistivity data. 

The low-pass filter used a wavelength cutoff spanning 10 data 

points (or a depth interval of 1 ft, 0.3 m).

Induction Log

Conductivity readings from the induction tool were 

inverted to resistivity values for comparison to the normal 

resistivity logs (fig. 11). The resulting resistivities appeared 

much too low, likely due to tool calibration problems. On the 

other hand, individual features of the induction curve show 

remarkable similarity to the 16-in. normal resistivity curve. 

Scatter plots comparing resistivity values for the two curves 

show a linear relation below 120 ft (36.5 m) but no observable relation shallower than this depth. Thus, to adjust for the 

calibration problem, the induction-tool resistivity values were 

scaled using a match to the 16-in. normal curve below 120 ft 

(36.5 m) depth as the criteria. The resulting transform applied 

to the induction-tool resistivity Rind to get a corrected Rcorr was 

computed in ohm-meters as

Rcorr = 3.75 Rind + 3.3.

Figure 11 shows the resistivity curves from the induction 

tool before and after scaling and after a low-pass filter was 

applied. The curves are shown in comparison to the normal 

resistivity curves after they were corrected and filtered.

Why the induction-tool resistivities and the normal 

resistivities have no apparent relation shallower than 120 ft 

(36.5 m) is unknown. Resistivities derived from a time-domain 

electromagnetic (TEM) sounding that was measured at the 

site before drilling suggest the problem lies with the induction 

log (fig. 12). The TEM model (D.V. Fitterman, USGS, unpub. 

data, 2009) is derived by assuming there are only four layers 

of different resistivity in the subsurface. The resistivities of 

each model layer, depicted by the straight vertical lines on 

figure 12, are a broad representation of the resistivities of the 

formation and pore fluids together. The TEM model matches 

the borehole resistivity curves fairly well below the depth of 

120 ft (36.5 m). The TEM model matches the normal resistivity curves better than the induction-tool resistivity curve above 

this depth. Interestingly, the 120-ft depth is close to the top of 

the confining clay layer at 119 ft (36.3 m), suggesting that the 

explanation is related to differences in the formation fluids in 

the unconfined and confined aquifers. However, this line of 

reasoning is contradicted by considering that borehole fluid 

affects the normal resistivity measurements more than those of 

the induction tool (table 4).

Density and Sonic Logs

After reviewing the original readings from the two density sensors (short-spaced and long-spaced), it was determined 

that density values were too low for the known lithology, and 

the tool calibration was not accurate. In 2013, the two sensors 

were calibrated at the USGS Texas Water Science Center in 

Austin, Texas, by measuring two reference blocks with known 

densities (aluminum and nylon with densities of 2.62 grams 

per cubic centimeter [g/cm3] and 1.24 g/cm3, respectively). 

This new calibration was then applied to the original log to 

provide an accurate, compensated bulk density log. A low-pass 

filter was applied to the compensated density log resulting 

from the calibration, which is shown in figure 13 alongside the 

sonic (seismic P-wave) velocity derived from the full waveform sonic log by Burke (2011). These density and sonic logs 

are best used to provide average values of bulk density and 

sonic velocity for shallow sediments of the San Luis Valley as 

opposed to detailed information about variations in lithology 

in the well. Sonic velocities average 5,922 ft/s (1,805 m/s) 

(Burke, 2011), with a standard deviation of 230 ft/s (70 m/s). 

The average and standard deviation from the compensated 

density log, not considering excursions at 80 and 135 ft (24.4 

and 41.4 m) and values measured within the PVC casing, are 

1.97 g/cm3 (1,970 kilograms per cubic meter [kg/m3]) and 

0.12 g/cm3 (120 kg/m3), respectively. These measurements 

are compatible with Gardner’s empirical relation between 

sonic velocity and bulk density in sedimentary basins (Gardner and others, 1974), in which a sonic velocity of 5,922 ft/s 

(1,805 m/s) relates to a density of 2.02 g/cm3 (2,020 kg/m3).
22 Sample Descriptions and Geophysical Logs for Cored Well, Great Sand Dunes National Park, Colorado

Figure 10. Normal resistivity curves from the multiparameter tool before and after data processing. Normal resistivities were 

corrected for borehole parameters, then spike-rejection and low-pass filters were applied.

EXPLANATION

10 100

16-in. normal

10 100

64-in. normal

0

40

60

80

100

0

50

0

50

150

200

250

300

100

150

200

250

300

100

Resistivity, ohm-meters Resistivity, ohm-meters

10

30

50

70

90

0

40

60

80

100

10

20 20

30

50

70

90

64-in. normal resistivity

64-in. normal resistivity 

after data processing

16-in. normal resistivity

16-in. normal resistivity 

after data processing

Base of polyvinyl 

chloride (PVC) casing

Depth, in feet

Depth, in meters

PVC casing
Geophysical Logs 23

Figure 11. Resistivity derived from the induction tool before and after data processing 

compared to normal resistivity curves after data processing. The induction-tool resistivity curve 

was scaled to the 16-in. normal resistivity curve.

10 100

10 100

0

50

150

200

250

300

100

Resistivity, ohm-meters

0

40

60

80

100

10

20

30

50

70

90

Depth, in meters

PVC casing

EXPLANATION

Resistivity from induction tool after 

data processing

64-in. normal resistivity after 

data processing

Resistivity from induction tool

16-in. normal resistivity after 

data processing

Base of polyvinyl chloride (PVC) casing

Depth, in feet
24 Sample Descriptions and Geophysical Logs for Cored Well, Great Sand Dunes National Park, Colorado

Figure 12. Resistivity curves after data processing compared to resistivity layers derived from a 

time-domain electromagnetic (TEM) sounding measured at the site before drilling (D.V. Fitterman, 

U.S. Geological Survey, unpub. data, 2009). The TEM model is derived by assuming there are only 

four layers of different resistivity in the subsurface.

EXPLANATION

Resistivity from induction tool 

after data processing

64-in. normal resistivity after 

data processing

16-in. normal resistivity after 

data processing

Model from transient electromagnetic (TEM) sounding

Base of polyvinyl chloride (PVC) 

casing

0

50

150

200

250

300

100

Resistivity, ohm-meters

0

40

60

80

100

10

20

30

50

70

90

Depth, in meters

PVC casing

10 100 1,000

Depth, in feet
Geophysical Logs 25

Figure 13. Sonic velocity and compensated density logs.

EXPLANATION

1,500 2,500

Meters per second

Sonic

1.00 2.00

Grams per cubic

centimeter

Density

Depth, in meters

Depth, in feet

Compressional sonic velocity derived 

from sonic log from Burke (2011)

Compensated density log after data 

processing

Base of polyvinyl chloride (PVC) casing

0

150

200

250

300

100

0

40

60

80

100

10

20

30

50

70

90

PVC casing
26 Sample Descriptions and Geophysical Logs for Cored Well, Great Sand Dunes National Park, Colorado

Digital Log Files

Digital files containing the final, processed data measured by the six borehole tools are available in American 

Standard Code for Information Interchange (ASCII) format, 

in the Downloads folder. The data files follow the Log ASCII 

Standard (LAS) for well logging established by the Canadian 

Well Logging Society (2011). The files can be read directly by 

many standard well logging software packages, imported into 

spreadsheet formats, or opened as an ASCII text file.

Summary of Findings

To serve as a foundation for future research using 

BP-3-USGS, we developed a generalized lithologic log and 

selected those borehole geophysical logs that demonstrate the 

most significant variations to use in comparison (fig. 14). The 

sample descriptions and their inferred depth positions in the 

well (fig. 7; appendix 1) were combined with general pattern 

changes observed mainly in the resistivity (16-in. normal and 

derived induction-tool logs), gamma-ray, neutron, and SP logs 

(figs. 8–11) to generalize the lithology across intervals greater 

than 1 foot. Uncertainties and limitations in determining the 

lithology with depth vary widely according to the conditions 

encountered during drilling, sampling, logging, and prolonged 

storage. These problems, and unresolved problems with 

calibrations of the resistivity data in particular, are described 

in detail in previous sections. The uncertainties and limitations 

suggest the positions of lithologic contacts on the interpreted 

generalized log are approximate but still adequate to represent 

a general view of the lithologic variations in the well. 

Overall, the generalized lithologic log shows three main 

packages: (1) mostly sand from the surface to about 77 ft 

(23.5 m) depth; (2) interbedded sand, silt, and clay decreasing in overall grain size downward from 77 to 232 ft (23.5 to 

70.7 m) depth; and (3) thick intervals of massive clay alternating with fine sand to silt from 232 to 326 ft (70.7 to 99.4 m) 

depth, which is the total depth of the well. Because artesian 

flow was observed only after drilling through the base of a 

clay-rich layer within the second lithologic package from 119 

to 134 ft (36.3 to 40.8 m) depth, we infer that the base of this 

clay-rich layer marks the top of the confined aquifer at an 

elevation of 7,415 ft (2,260 m) above sea level.

The top 77 ft (23.5 m) of mostly sand is compatible with 

the history of an alluvial-fan environment followed by eolian 

deposition after the disappearance of Lake Alamosa. The 

contact between eolian and alluvial-fan deposits, which has 

been observed in wells elsewhere (Madole and others, 2008), 

is not well defined from our lithologic descriptions (appendix 1). Observations of mature, well-sorted sand observed 

from 0 to 20 ft (0 to 6 m) depth and poorly sorted, dominantly 

coarse-grained sand at 40 ft (12 m) depth (appendix 1) suggest 

that the contact lies somewhere between 20 and 40 ft (6 and 

12 m) depth.

The middle lithologic package, between 77 to 232 ft 

(23.5 to 70.7 m) depth, is represented by a heterogeneous mix 

of clastic sediments with a wide range of grain sizes (fig. 14), 

although grain sizes are generally finer below 150 ft (46 m) 

than above this depth. The lithologic heterogeneity is mimicked by the large variability in the curves of the borehole logs 

(fig. 14). A general decrease in grain size with depth is supported by an overall decrease in resistivity. Two thick clay-rich 

layers at 77–80 ft (23.5–24.4 m) and 119–134 ft (36.3–40.8 m) 

are actually a mixture of clay and coarser grained material 

(appendix 1). The well began flowing after drilling had penetrated the base of the deeper clay-rich interval. Freshwater 

fossils and evidence of bioturbation are common in the clayrich layers found throughout this lithologic package. Notable 

is the occurrence of lacustrine diatoms in the topmost clay-rich 

layer (fig. 14; appendix 2), suggesting that even the youngest 

deposits of this package accumulated in a lacustrine environment. The interbedded heterogeneous nature of this succession 

and the relative abundance of freshwater fossils are compatible with the history of a transitional Lake Alamosa that was 

expanding and contracting before it completely disappeared. 

Alternatively, the heterogeneity could represent an environment of intermittent lake development that was localized near 

the well site, especially in the interval above 150 ft (45.7 m). A 

calcite-cemented sand layer at 181–191 ft (55.2–58.2 m) might 

represent one of the laterally extensive, poorly cemented sand 

layers described by Brister and Gries (1994), which they interpret as marking the beginning of the demise of Lake Alamosa.

The clay layer encountered at 232 ft (70.7 m) depth 

marks the top of the lowermost lithologic package, which is 

dominated by thick clay layers and intervening fine sand to 

silt. The blue tint to this clay and to clay in the interval from 

254 to 276 ft (77.4 to 84.2 m) suggests one or both of these 

layers represent the blue clay that is observed in water wells 

throughout the San Luis Valley. However, this blue clay does 

not correspond to the top of the confined aquifer that is sometimes presumed elsewhere in the valley (Huntley, 1979a). The 

blue tint of the top two clay intervals was notably different 

from the more even gray color of the lower clay interval below 

294 ft (89.6 m) when observed in the field, evident now only 

from photographs (fig. 6). The variation in color may indicate 

a difference in the chemistry of the depositional environments. Abundant fossils in all the clay layers of the lowermost 

lithologic package attest to a thriving lacustrine environment, 

which likely received debris from animals and plants that 

lived on land nearby. The intervals of sand deposition at well 

depths of 276–295 ft (84.1–89.9 m) and possibly 241–254 ft 

(73.5–77.4 m) may represent shifts in the position of the lake 

basin that persisted for significant periods of time.

Several apparent discrepancies between the borehole logs 

and the generalized lithologic log, which have different implications, are evident upon examination of figure 14. First, the 

resistivity values derived from the induction tool appear to be 

too low in comparison to what is expected for the dominantly 

sand intervals above 120 ft (36.6 m). For example, coarser 

grained sand intervals containing fresh water in the upper part 
Summary of Findings 27 Figure 14. Selected geophysical logs and generalized lithologic log for BP-3-USGS. Only clay layers thicker than 1 ft (0.3 m) are depicted. Water flowing out of the drill stem was observed once the clay-rich layer between depths of 119 and 134 ft (36.3 and 40.8 m) had been penetrated (labeled “Begin flow”).The well continued to flow as drilling continued below this depth (fig. 2

E), but the flow was not measured nor water sampled. The static water level is inferred from neighboring well BP-3 

(HRS Water Consultants, Inc., 2009). The top of the interval labeled “Electrical conductor” corresponds to the depth of a conductive layer, similar to that detected in geophysical surveys throughout the region. Uncertainties about the lithology inferred within depth interval 241–254 ft (73.5–77.4 m) are discussed in the text.

10 100 1,000

Resistivity

Ohm-meters

16-in.normalFrom inductiontool

020406080100

Depth, in meters

100 200

Gamma

Counts per second

500 1,000 1,500

Neutron

Counts per second

SP

-50 0

Millivolts

0

50

150200250300

Depth, in feet

100

Polyvinyl chloride

Washout Washout 

Tight hole

Static water

(PVC) casinglevel from BP-3

Begin flow

clayclay, ash shardsclayclayclay

Sand lithified with calcite cement. BivalvesMedium to fine sand. Lithified?Blue-gray clay with silty intervals. Abundant 

lacustrine fossils

Fine sand to silt, with many thin clay layers, 

brackish water, or both?

Massive blue-gray clay with laminations and a 

few thin silty to sandy layers. Abundant lacustrine fossils. Diatoms

Fine sand to silt with clay layerMassive gray clay with a few thin silty to 

sandy layers. Abundant lacustrine fossils

Fine sand to silt with clay layers. Ostracods in 

lower part.Fine sand to silt with clay layers. 

Lacustrine fossils

Coarse to fine sand with abundant dark grainsSilty clay?Coarse to fine sand

Interbedded clay, silt, and fine sand. Diatoms

Sand with thin silt and clay layers

Interbedded clay, silt, and fine sand 

Medium to fine sand

Lithology

?

Coarse sand, with additional fine sand in 

lower part

50

100150

Depth, in feet

200250300

020406080100

Depth, in meters

0

Elevation

7,549 ft

(2,301 m)

Electrical

conductor
28 Sample Descriptions and Geophysical Logs for Cored Well, Great Sand Dunes National Park, Colorado

of the well (for example, 10–50 ft [3.0–15.2 m]) should have 

higher resistivities than those with finer grained sand lower in 

the well (for example, 282–295 ft [86.0–89.9 m]) rather than 

about the same resistivities, as indicated by the inductiontool resistivity curve (green curve on the resistivity panel of 

fig. 14). This problem has already been noted in comparison 

to the normal resistivity logs, but the normal resistivity logs 

cannot be compared above 67 ft (20.4 m) where the well is 

cased. For readings above 67 ft (20.4 m), the predominance 

of sand in well samples supports the supposition that the 

induction-tool resistivities are also too low above 67 ft. Thus, 

the induction-tool resistivities should not be used to characterize the resistivities of the lithologies within the entire interval 

from the surface to 120 ft (36.6 m) depth. Interestingly, the top 

of the confining clay layer occurs near the problem depth of 

120 ft (36.6 m), suggesting that the issues with the inductiontool data somehow correspond to the extent of the unconfined 

aquifer. However, understanding a physical relation for this 

correspondence remains elusive.

Second, the gamma-ray log shows apparent discrepancies with the generalized lithologic log. The patterns of the log 

curve do not have good correlation to variations in clay versus 

sand and are generally high throughout the well. Commonly, 

high gamma values correspond to clays and low values to 

sands (Keys, 1990, 1997; table 4). For example, gamma-ray 

values within the depth interval 119–150 ft (36.3–45.7 m) are 

highly variable but do not show the clear difference in pattern 

between the clay above and sand below that is evident from 

the well samples and the other geophysical logs (fig. 14). The 

discrepancy with the gamma-ray log may be caused by volcanic clasts that are prevalent in sands in this area (Madole and 

others, 2013). Volcanic clasts likely have abundant potassium 

feldspar and thus increased radioactivity because of the high 

potassium content (Keys, 1997).

Finally, a discrepancy between all the geophysical logs 

and the generalized lithologic log occurs between depths 241 

and 254 ft (73.5 and 77.4 m), which has significance for future 

studies. Fine sand to silt is indicated for all but two thin (a foot 

or less) layers of clay from the drilling speed and from the 

accompanying bucket sample for 241–251 ft (73.5–76.5 m) 

(appendix 1). This presumed sandy interval is sandwiched 

between the two blue-colored clay layers, suggesting that the 

geophysical logs should have significantly different character across this interval compared to the clay layers. Instead, 

the SP, neutron, and resistivity logs do not show significant 

changes in character across the entire sequence of clays and 

intervening sand to silt (fig. 14), suggesting the whole interval 

is mostly clay. The gamma-ray log is highly variable across 

the whole interval, with no clear pattern differences that match 

the lithologic contacts. Density and sonic velocity logs show a 

gradual, very slight decrease across the entire sequence, with a 

minimum at the middle of the presumed sandy layer (fig. 13). 

The most striking lack of response to the presumed sandy 

layer comes from the resistivity curve because variations in 

these data correlate well to differences in sand versus clay 

content in most of the rest of the well. Even if one assumes 

maximum error in the depth positioning of core samples, the 

base of the clay above and the top of the clay below the presumed sandy layer are well constrained (fig. 7), with no more 

than 4 ft (1.2 m) of error.

The high conductivity (low resistivity) of the presumed 

sandy interval at 241–254 ft (73.5–77.4 m) might be explained 

by (1) water contained within a sandy layer that is high in 

total dissolved solids, such as salt; or (2) a greater clay content 

than expected within the interval that did not affect drilling speed and was not captured in the core barrel. The first 

hypothesis explains the on-site and sampling evidence and 

the resistivity logs but is contradicted by the responses of the 

other geophysical logs. The second hypothesis explains the 

responses of the geophysical logs but is contradicted by inferences made from the drilling speed and lack of recovery of 

any clay-rich material. Possible support for the first hypothesis 

is the slight separation between the induction-resistivity log 

and 16-in. short-normal resistivity curves over this interval 

(fig. 14) where the induction-tool resistivities show lower 

values. Because the 16-in. short-normal tool has less penetration and is more affected by drilling fluid than the induction 

tool (table 4), the lower values in the induction-resistivity log 

suggest that the formation fluid is more conductive than the 

drilling fluid, which may indicate saline fluid trapped within 

this interval. However, water from the confined aquifer in 

two deep wells located about 7 mi (11 km) to the northeast 

of BP-3-USGS does not show anomalously high specific 

conductance nor high sodium levels (Rupert and Plummer, 

2004). If instead the second hypothesis is true, it is mainly 

contradicted by the dominance of sand over clay that was 

inferred from the drilling speed (appendix 1). Because of the 

limitations of bucket samples discussed earlier, and the low 

volume of material returned in the bucket for the interval 

241–251 ft (73.5–76.5 m) (appendix 1), evidence of fine sand 

to silt in the bucket sample may be misleading. Perhaps drilling through multiple, thin clay layers dispersed throughout a 

fine-grained sandy interval might feel as though the material 

were mostly sand.

Significance for Future Studies

The unique location and setting of BP-3-USGS allow 

for future study that can test hypotheses developed from the 

geophysical studies and address questions about the nature and 

history of Lake Alamosa. The data from this report, combined 

with preliminary data from several previous studies, suggest 

promising directions for determining depositional environment 

through time, improving the understanding of the nature of the 

confined aquifer, and allowing for integrated interpretation of 

the aerially extensive geophysical surveys in the area.

Preliminary paleomagnetic measurements indicate that 

the core samples record a magnetic reversal near the top of the 

first blue clay layer, tentatively correlated with the 0.78-Ma 

Brunhes-Matuyama boundary (Davis and others, 2013). These 
Significance for Future Studies 29

findings suggest that ages for other intervals of the well can 

be extrapolated from this interval by determining reasonable 

sedimentation rates. Volcanic ash shards found in several 

intervals should be evaluated for age dating or tephrochronologic correlation to samples of known age. Obtaining ages at 

these intervals would better establish the chronology of the 

well stratigraphy, confirm the paleomagnetic results, and allow 

correlation with similar results from outcrop and core samples 

studied at Hansen Bluff, 24 mi (38 km) to the south (fig. 1) 

(Rogers and others, 1992; Machette and others, 2007).

Once age is estimated, more detailed studies of the 

samples could yield information about depositional environment through time. The strategic approach of the studies 

might follow that of the Hansen Bluff studies. Variations 

noted in species of ostracods, pollen, fish, and vertebrates in 

these studies indicated periods of warm versus cold climate 

(Rogers and others, 1992), which have potential for correlation with species present within BP-3-USGS. In particular, 

the warm-climate ostracod species Limnocythere bradburyi

makes up a coquina at the base of Hansen Bluff near a layer of 

Bishop Tuff ash (Rogers and others, 1992), which has an age 

of 774 kilo-annum (ka) (Sarna-Wojcicki and others, 2000). 

L. bradburyi was also identified in the blue clay at a depth of 

93 m in a deep water well 7 mi (11 km) to the northeast of 

BP-3-USGS (reported in Madole and others, 2013). If this species is also identified in the blue clay of BP-3-USGS, depositional environment might be correlated across a wide area. If 

the timing of these variations in environment can be estimated, 

the findings will have implications for geologic and climatic 

history for the San Luis Valley. Correlations with worldwide 

events and geologic mapping of the Rio Grande rift may lead 

to conclusions about the role of climate versus tectonics during geologic history.

Investigations of BP-3-USGS can also test hypotheses 

about when and how Lake Alamosa dried up after breaching its lava dam at about 440 ka (Machette and others, 2013). 

In question is whether sediments from depths of 77–119 ft 

(23.5–36.3 m), which lie above the confining clay layer, 

represent transgressions and regressions of Lake Alamosa or 

whether they were deposited in a local setting with less significance, such as a fluvial environment with migrating oxbow 

lakes. Preliminary examination of diatoms in the shallow 

clay layer at 77 ft (23.5 m) depth (fig. 14; appendix 2) indicates a strong presence of a species resembling Aulacoseira 

distans that is known to inhabit small, acidic lakes (Florin, 

1981; Camburn and Kingston, 1986; Haworth, 1988; Siver 

and Kling, 1997; Camburn and Charles, 2000). The genus 

Stephanodiscus was also observed in the clay layer, which is 

a common planktonic form in lakes, ponds, and large rivers 

(Stoermer and Julius, 2003). Combined with age estimates, 

these findings may provide evidence for a revised time frame 

for the demise of Lake Alamosa.

Diatoms were anticipated in a number of other intervals 

throughout the core; a few were sampled (appendix 2). One 

additional interval that yielded diatoms was the blue clay at 

261–266 ft (79.6–81.1 m) depth. Preliminary examination 

of a sample from this interval revealed not only specimens 

resembling Aulacoseira distans, but also a species resembling Anomoeoneis sphaerophora f. costata that inhabits 

high-conductance and brackish waters (Kociolek and Spaulding, 2003) and is among species that are prevalent in highly 

alkaline waters (Schmid, 1977). Additional pennate diatoms 

were also observed. Though appearing contradictory as to the 

suggested nature of the lake setting, the importance of this 

find is that one could interpret the specimens of Anomoeoneis

as suggestive of a nearby shoreline habitat that had migrated 

closer to the borehole location due to lake drawdown. Such 

evidence could have implications for the paleoclimate, the 

basin geometry, or the regional tectonics. Because no diatoms 

were discovered in samples from Hansen Bluff (Rogers and 

others, 1992), the documented presence of diatoms in the 

BP-3-USGS core presents a unique opportunity for a more 

systematic diatom study that could assist with future interpretations of the lake history.

Although BP-3-USGS was not drilled to investigate 

hydrology, two results are significant or worth further study. 

First, establishing the top of the confined aquifer adds valuable information for regional groundwater models of the area, 

given the paucity of wells penetrating the confined aquifer in 

Great Sand Dunes National Park and Preserve (Rupert and 

Plummer, 2004). Second, the alternate hypotheses to explain 

the conflict in geophysical log response across the apparent 

sandy interval at 241–254 ft (73.5–77.4 m) requires further 

evaluation. Follow-up work would likely focus on additional 

processing of the geophysical logs and evaluation of other 

deep wells in the region because core was not recovered from 

this interval.

Finally, the three general lithologic packages observed 

in the well have good correspondence to the resistivity model 

determined from the time-domain EM sounding acquired 

before drilling (fig. 12). A resistive (>80 ohm-m) layer above 

85 ft (25.9 m) depth corresponds well to the upper package of 

mostly sand, with the uppermost, very resistive 15 ft (4.6 m) 

perhaps representing unsaturated sand. A 20-ohm-m model 

layer extending from 85 to 235 ft (25.9 to 71.6 m) corresponds 

well to the middle interbedded sand, silt, and clay package. 

Most importantly, the low resistivities (high conductivities) 

of the lowermost model layer, which is also shown by the 

resistivity logs (fig. 12), mark the top of the lowermost package containing thick clay layers. Similar model resistivity 

layers have been observed throughout the park and vicinity in 

both ground-based and airborne EM surveys (Fitterman and 

Grauch, 2010; Bedrosian and others, 2012). Most notably, 

BP-3-USGS supports the hypothesis that the persistent, strong 

electrical conductor observed in the geophysical surveys 

corresponds to the top of the first observance of massive blue 

clay. This confirmation allows future studies to use the electrical conductor as a proxy to correlate this regional clay across a 

much wider area. Moreover, if the low resistivity (high electrical conductivity) of the sandy interval between the two blue 

clay layers in BP-3-USGS is caused by saline water, locating 

the electrical conductor from geophysical surveys may also 
30 Sample Descriptions and Geophysical Logs for Cored Well, Great Sand Dunes National Park, Colorado

locate this unusual layer elsewhere, where its nature can be 

tested.

Acknowledgments

We thank the USGS Central Region drilling and logging 

team (Art Clarke, Jeff Eman, Steve Grant, Mike Williams, 

Derek Gongaware, and Barbara Corland) for their expertise, 

good humor, and invaluable help. We are indebted to Harland 

Goldstein (USGS) for his critical support in the sampling 

operations and field work. We thank Andrew Valdez (NPS) 

and Fred Bunch (NPS) for their help and advice at the drill 

site. Invaluable assistance was provided by USGS scientists 

Janet Slate and Mark Hudson in preliminary evaluations of 

the well samples and Phil Nelson, Bruce Smith, and especially 

Greg Stanton, in processing the geophysical logs. We are 

grateful to HRS Water Consultants, who generously provided 

advice and information. We appreciate the logistical support 

and collaboration of the Water Resources Division of NPS, in 

particular, Jim Harte. Finally, we appreciate the funding and 

moral support for this serendipitous endeavor by the National 

Cooperative Geologic Mapping Program, especially Randy 

Orndorff (USGS).

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Appendixes
34 Sample Descriptions and Geophysical Logs for Cored Well, Great Sand Dunes National Park, Colorado Appendix 1. Descriptions of samples by type and drilling interval. [Drilling depth interval, interval evaluated for sampling; those sampled for core are indicated by the core run number; depths listed in feet (ft), corresponding to drilling procedures; m, meters. Sample types described in text and table 1. N/A, not applicable. XRD, X-ray diffraction. Analyses are presented in appendix 3. Onsite core recovery length is the original length measured in 2009. Cores are logged from bot- tom (0.0 ft) to the top of the sample relative to core lengths measured in 2013, which could be different than the onsite length (table 2). See appendix 2 for more detail on fossil and trace fossil observations.] Drilling depth interval Description from drilling speed and onsite observations Descriptions of mud stream samples Descriptions of core barrel samples 0–20 ft (0–6.1 m) Rotary drilling Coarse sand with clumps of silty clay Sieved cuttings at 10 ft. Coarse sand to clay with poorly sorted subrounded to rounded, mostly dark grains. Slightly calcareous. Sieved cuttings at 20 ft. Coarse to fine sand with rounded to subrounded grains. Noncalcareous. Hopper samples (coarse and fine fractions) from 0–20 ft. Coarse to very fine sand with subrounded to rounded, mostly dark grains. About twice the volume of coarse- compared to fine-grained fraction. Very mature. Slightly calcareous. N/A 20–40 ft (6.1–12.2 m) Rotary drilling Coarse sand with clumps of green clay grading downward to fine sand Hopper samples (coarse and fine fractions) from 20–30 ft. Coarse to fine sand with rounded to subrounded, mostly dark grains. Noncalcareous. Sieved cuttings at 30 ft. Coarse to fine sand with rounded to subrounded, mostly dark grains. Noncalcareous. Hopper samples (coarse and fine fractions) from 30–40 ft. Coarse to fine sand with subangular to rounded, mostly dark grains. Noncalcareous. Sample taken from fine fraction for XRD analysis Sieved cuttings at 40 ft. Very coarse to fine sand, dominated by coarse sand. Poorly sorted, subangular to rounded, mostly dark grains, some volcanic grains. Noncalcareous. N/A
Appendixes 35

Drilling depth 

interval

Description from drilling speed 

and onsite observations

Descriptions of mud stream samples Descriptions of core barrel samples

40–60 ft(12.2–18.3 m)Rotary drilling

Fine to coarse sand with 

clumps of clay at 60 ft

Hopper samples (coarse and fine fractions) from 40–50 ft.

Coarse to fine sand with subangular to rounded, mostly dark 

grains and some pebbles. Noncalcareous.

Sieved cuttings at 50 ft.

Coarse to fine sand with subrounded to rounded, mostly dark 

grains. Slightly calcareous.

Hopper samples (coarse and fine fractions) from 50–60 ft.

Coarse to very fine sand with subangular to rounded, dark 

grains. Poorly sorted.

Sieved cuttings at 60 ft.

Coarse to fine sand with subangular to rounded grains. Some 

magnetic grains, some volcanic grains, some biotite. Maybe some volcanic glass. Noncalcareous.

Hand sample of clay and sand at 60 ft.

Coarse to fine sand, subangular to rounded grains, poorly 

sorted. Not much clay.

N/A

60–70 ft(18.3–21.3 m)Core run 1

Sand with clay from 60–68 ft N/A Viscous fluid sample, sieved.

Very coarse to fine sand with poorly sorted, subangular 

to rounded grains. Abundant dark grains. Noncalcareous. Sieving may have removed silts and clays. Support for silty clay in the interval 60–65 ft comes from slight drop in resistivity from induction log and nearby BP-3 well where silty clay was logged from 60–66 ft. Other logs cannot be evaluated because this interval is mostly inside the casing.

70–80 ft(21.3–24.4 m)Core run 2

Sand with clay layer at 77 ft N/A Core catcher sample (probably from 77 ft).

Very fine sand to silt interbedded with clay. Sand and silt 

have angular to subrounded, well-sorted grains and tan color, mostly quartz. Not as many dark grains compared to intervals above. Calcareous. Clay is greenish-gray, very calcareous. Some beds are fine sand to clay. Geophysical logs and lithology in neighboring BP-3 well indicate the fine-grained interval extends from 77–80 ft. Two samples taken for XRD analysis. Diatoms.

Appendix 1. Descriptions of samples by type and drilling interval.—Continued[Drilling depth interval, interval evaluated for sampling; those sampled for core are indicated by the core run number; depths listed in feet (ft), corresponding to drilling procedures; m, meters. Sample types described in text and table 1. N/A, not applicable. XRD, X-ray diffraction. Analyses are presented in appendix 3. Onsite core recovery length is the original length measured in 2009. Cores are logged from bottom (0.0 ft) to the top of the sample relative to core lengths measured in 2013, which could be different than the onsite length (table 2). See appendix 2 for more detail on fossil and trace fossil observations.]
36 Sample Descriptions and Geophysical Logs for Cored Well, Great Sand Dunes National Park, Colorado Drilling depth interval Description from drilling speed and onsite observations Descriptions of mud stream samples Descriptions of core barrel samples 80–90 ft (24.4–27.4 m) Core run 3 Coarse sand with a little hard, dark clay N/A Core catcher sample (possibly from 85 ft, based on geophysical logs). Very fine sand to clay, mostly silt with very little coarse sand. Well-sorted angular to subangular grains. Fewer dark grains than above, some mica. Noncalcareous. Sample taken for XRD analysis. 90–92 ft (27.4–28.0 m) Core run 4 Dark-gray silty clay and fine sand with layer-like chunks of lime-green clay Sieve sample at 92 ft. Coarse to fine sand, angular to rounded grains, poorly sorted. Some mica, one large potassium feldspar grain. Very calcareous. Core catcher plus viscous fluid samples, sieved. Very fine sand to silt, some coarse sand, not much clay, if any. Mostly quartz. Lots of mica. Medium to well sorted. Slightly calcareous. 92–94 ft (28.0–28.7 m) Core run 5 Sand with layer-like chunks of green clay N/A Viscous fluid sample, scooped. Medium to very fine sand, subangular to rounded grains. Some clumps of blue clay. Medium sorting. Slightly calcareous. Core catcher sample. Coarse sand to silt, poorly sorted. Mostly quartz grains with some potassium feldspar, relatively few dark grains, some magnetite grains. Very calcareous. 94–96 ft (28.7–29.3 m) Core run 6 Clay above medium, dark gray sand N/A Core catcher sample (probably from 94 ft). Fine sand to clay with well-sorted, angular to subrounded grains. Clumps of tan clay. Some clumps of medium sand with darker grains. Noncalcareous. 96–101 ft (29.3–30.8 m) Core run 7 Sand N/A Viscous fluid sample, sieved. Coarse to very fine sand with medium-sorted, subangular to rounded dark grains. Noncalcareous. Core catcher sample (probably from 101 ft). Fine sand to silt with very well-sorted, subangular to rounded grains. Moderately abundant dark grains. Noncalcareous. Appendix 1. Descriptions of samples by type and drilling interval.—Continued [Drilling depth interval, interval evaluated for sampling; those sampled for core are indicated by the core run number; depths listed in feet (ft), corresponding to drilling procedures; m, meters. Sample types described in text and table 1. N/A, not applicable. XRD, X-ray diffraction. Analyses are presented in appendix 3. Onsite core recovery length is the original length measured in 2009. Cores are logged from bot- tom (0.0 ft) to the top of the sample relative to core lengths measured in 2013, which could be different than the onsite length (table 2). See appendix 2 for more detail on fossil and trace fossil observations.]
Appendixes 37

Drilling depth 

interval

Description from drilling speed 

and onsite observations

Descriptions of mud stream samples Descriptions of core barrel samples

101–119 ft(30.8–36.3 m)(No core sample)

Sand with thin layers of clay at 

115 ft and 119 ft

Sieve sample at 105 ft.

Coarse sand with medium-sorted, subangular to rounded 

grains. Abundant dark grains. Noncalcareous.

Sieve sample at 112 ft.

Coarse sand with medium-sorted, subangular to rounded 

grains. Abundant dark grains. Noncalcareous.

Sieve sample at 115 ft.

Coarse sand with medium-sorted, subangular to rounded 

grains. Abundant dark grains. Noncalcareous.

Sieve sample at 119 ft.

Coarse to fine sand with poorly sorted, subangular to rounded 

dark grains. Noncalcareous.

N/A

119–125 ft(36.3–38.1 m)Core run 8

Clay with sand gradually 

increasing downward 

N/A Core piece (1.6 ft fell off core table, probably from 119–121 ft).

Fine sand to clay with subangular to rounded grains. Sandy 

clay interbedded with sand layers. Noncalcareous.

Core catcher sample.

Fine sand to silt with well-sorted, angular to subrounded 

grains. Moderately abundant dark grains. Noncalcareous, although light-colored pockets are calcareous. Sample taken for XRD analysis.

125–128 ft(38.1–39.0 m)Core run 9

Clay N/A Core (1.0 ft onsite recovery, probably from 125–126 ft).

0.5–1.0 Dark gray silty clay with fewer dark grains in the 

finer material. Slightly calcareous. 

0.0–0.5 Light gray sandy clay. Sand consists of abundant 

dark grains. Slightly calcareous. Faintly bedded. Dessication cracks parallel to bedding.

Core catcher sample.

Medium well sorted silt to clay, with very little silt. Some mica. Noncalcareous.

128–131 ft(39.0–39.9 m)Core run 10

Clay changing to sand below 

129 ft 

N/A Core catcher sample (probably from 128–129 ft).

Fine sand to clay, mostly silt, with medium sorted, 

subangular to rounded dark grains. Very calcareous.

Appendix 1. Descriptions of samples by type and drilling interval.—Continued[Drilling depth interval, interval evaluated for sampling; those sampled for core are indicated by the core run number; depths listed in feet (ft), corresponding to drilling procedures; m, meters. Sample types described in text and table 1. N/A, not applicable. XRD, X-ray diffraction. Analyses are presented in appendix 3. Onsite core recovery length is the original length measured in 2009. Cores are logged from bottom (0.0 ft) to the top of the sample relative to core lengths measured in 2013, which could be different than the onsite length (table 2). See appendix 2 for more detail on fossil and trace fossil observations.]
38 Sample Descriptions and Geophysical Logs for Cored Well, Great Sand Dunes National Park, Colorado Drilling depth interval Description from drilling speed and onsite observations Descriptions of mud stream samples Descriptions of core barrel samples 131–141 ft (39.9–43.0 m) Core run 11 Interbedded sand and clay, some black nodules (peat?) Bucket sample, 131–141 ft. Coarse sand to clay, with poorly sorted, angular to subrounded grains. Very few dark grains. Noncalcareous. Core (0.6 ft onsite recovery). 0.3–0.8 Medium sand to clay, mostly sand; abundant dark grains. Possible bioturbation from 0.7 to 0.8 ft; massive with no laminations elsewhere. Calcareous. 0.2–0.3 Coarse sand to clay, mostly sand. Slightly calcareous. 0.0–0.2 Fine sand to clay, mostly clay; fewer dark grains than above. Slightly calcareous. Core catcher sample (probably from 134 ft, based on geophysical and caliper logs). Fine sand to clay, mostly silt, with medium sorted, subangular to rounded dark grains. Noncalcareous. 141–151 ft (43.0–46.0 m) Core run 12 Sand, with less than 1-ft-thick layers of clay at 145 ft and 151 ft Bucket sample, 141–151 ft. Medium to fine sand, with well-sorted, subangular to rounded grains. Abundant dark grains. Noncalcareous. Core catcher sample (probably from 151 ft, based on geophysical logs). Fine sand to clay, with well-sorted, subangular to rounded grains. Clay is calcareous; fine sand is not. 151–161 ft (46.0–49.1 m) (No core sample) Fine sand with only a little clay Bucket sample, 151–161 ft. Fine sand to silt, with medium sorted, subangular to rounded grains. Quartz grains more abundant than dark grains. Noncalcareous. N/A 161–171 ft (49.1–52.1 m) (No core sample) Fine sand with a few thin clay layers Bucket sample, 161–171 ft. Fine sand to silt, with medium-sorted, subangular to rounded grains. Quartz grains more abundant than dark grains. Noncalcareous. N/A Appendix 1. Descriptions of samples by type and drilling interval.—Continued [Drilling depth interval, interval evaluated for sampling; those sampled for core are indicated by the core run number; depths listed in feet (ft), corresponding to drilling procedures; m, meters. Sample types described in text and table 1. N/A, not applicable. XRD, X-ray diffraction. Analyses are presented in appendix 3. Onsite core recovery length is the original length measured in 2009. Cores are logged from bot- tom (0.0 ft) to the top of the sample relative to core lengths measured in 2013, which could be different than the onsite length (table 2). See appendix 2 for more detail on fossil and trace fossil observations.]
Appendixes 39

Drilling depth 

interval

Description from drilling speed 

and onsite observations

Descriptions of mud stream samples Descriptions of core barrel samples

171–191 ft(52.1–58.2 m)Core run 13

Fine to coarse sand with clay 

layer at 175–176 ft and apparent clay layers at 180 ft, 187–188 ft, and 189–191 ft. The appearance of light-colored chunks along with higher values on the resistivity and density logs (examined later) suggest that slow drilling speeds were caused by lithified sand rather than clay within 181–191 ft

Bucket sample, 171–181 ft.

Fine sand to silt, with medium-sorted, subangular to rounded 

grains. Quartz grains more abundant than dark grains. Noncalcareous.

Bucket sample at 181–191 ft.

Fine sand to silt, with medium-sorted, subangular to rounded 

grains. Very slightly calcareous. Sample of clam shells collected.

Hand samples of light-colored chunks at 191 ft.

Coarse to fine sand with subangular to rounded grains. Most 

of the coarse particles are aggregates of fine sand cemented with calcium carbonate.

Core (4.0 ft onsite recovery, but core was in pieces that may not 

have been contiguous).

3.7–4.0 Abrupt transition at 3.7 ft from muddy sand 

below to dark greenish-gray clay above. Grades upward from noncalcareous to calcareous. This piece may not be contiguous with core below. 

2.7–3.7 Muddy sand. Calcareous.2.5–2.7 Grades upward from clay to muddy sand. 

Calcareous.

0.7–2.5 Greenish-gray clay with some silt, possibly from 

175–177 ft, based on drilling description and geophysical logs. Calcareous. A few ostracods at 1.7 to 2.0 ft. Rust colored stain in spots at 2.3 ft probably developed during sample storage.

Some core sample is presumed missing here. Assume core 

above and below are not contiguous based on attempts to match lithologies with geophysical logs.

0.0–0.7 Coarse to medium, light tan, very well sorted, fairly 

clean sand with calcareous cement. Faint laminations may have been caused by coring bit. Grades upward into clay. Probably from somewhere near the top of 186–191 ft from driller’s observations and geophysical logs.

Core catcher sample (probably from 191 ft based on hand 

collected sample.Fine sand to silt, with well sorted, subangular to rounded 

grains. Lithified with very calcareous cement.

Appendix 1. Descriptions of samples by type and drilling interval.—Continued[Drilling depth interval, interval evaluated for sampling; those sampled for core are indicated by the core run number; depths listed in feet (ft), corresponding to drilling procedures; m, meters. Sample types described in text and table 1. N/A, not applicable. XRD, X-ray diffraction. Analyses are presented in appendix 3. Onsite core recovery length is the original length measured in 2009. Cores are logged from bottom (0.0 ft) to the top of the sample relative to core lengths measured in 2013, which could be different than the onsite length (table 2). See appendix 2 for more detail on fossil and trace fossil observations.]
40 Sample Descriptions and Geophysical Logs for Cored Well, Great Sand Dunes National Park, Colorado Drilling depth interval Description from drilling speed and onsite observations Descriptions of mud stream samples Descriptions of core barrel samples 191–201 ft (58.2–61.3 m) Core run 14 Sand with clay layers at 193–198 ft and 201 ft Bucket sample, 191–201 ft. Fine sand to silt with well-sorted, subangular to subrounded grains. Noncalcareous. Core (3.2 ft onsite recovery). 2.7–3.1 Abrupt transition at 2.7 ft from clay below to medium-sorted, medium sand to silt with little clay above. Abundant dark grains. Calcareous. Similar to the sand from 0.0–1.3 ft but less well sorted. No bedding. 1.3–2.7 Greenish silty clay with very little silt, probably from 193–195 ft based on description and geophysical logs. Increases from calcareous at the bottom of the interval to very calcareous at the top. Shell at 2.3 ft. Sample collected for XRD analysis. 0.0–1.3 Very fine, olive-green sand to clay, with very little clay. Calcareous. Sand is well sorted with abundant dark grains. Clay content increases upward from 1.1–1.3 ft. No bedding. Sample collected for XRD analysis. Core catcher sample, possibly from 197 ft, based on logs. Fine sand to silt, with well-sorted, subangular to subrounded grains, including ash shards and magnetite. Noncalcareous. Bivalve fossil collected. 201–211 ft (61.3–64.3 m) Core run 15 Fine sand with clay at 201–202.5 ft and tighter clay at 205–207 ft Bucket sample, 201–211 ft (minimal material recovered). Coarse sand to silt with subangular, subrounded to rounded grains. Noncalcareous. A few glass shards. Some or all of the material may have come from a different depth interval. Core (1.7 ft onsite recovery). 0.2–1.7 Muddy silt with some fine sand. Well sorted, with not as many dark grains as below. Slightly calcareous. No bedding or laminations. Shell fragment. 0.0–0.2 Silt to clay with dark grains. Slightly calcareous. Abrupt transition from silty clay to muddy silt above. No bedding or laminations. Core catcher sample, probably from 207 ft, based on logs. Silt to clay with some small gypsum crystals. Calcareous. 211–221 ft (64.3–67.4 m)

Core run 16

Sand with greenish sandy clay 

at 211–214 ft

Bucket sample, 211–221 ft.

Coarse sand to silt with medium-sorted, subangular to 

rounded grains. Abundant dark grains. Calcareous.

Core (2.2 ft onsite recovery).

0.0–2.2 Sand to clay, with very little fine sand, mostly silt. 

Calcareous. Ostracod, clam, and unknown shell fragments from 1.4 to 2.1 ft. Some small magnetic black blotches from 2.0 to 2.2 ft.

Core catcher sample, probably from 215 ft, based on logs.

Fine sand to gray-green clay. Calcareous. Bivalve fragments. 

Fish bones(?) sampled. 

Appendix 1. Descriptions of samples by type and drilling interval.—Continued[Drilling depth interval, interval evaluated for sampling; those sampled for core are indicated by the core run number; depths listed in feet (ft), corresponding to drilling procedures; m, meters. Sample types described in text and table 1. N/A, not applicable. XRD, X-ray diffraction. Analyses are presented in appendix 3. Onsite core recovery length is the original length measured in 2009. Cores are logged from bottom (0.0 ft) to the top of the sample relative to core lengths measured in 2013, which could be different than the onsite length (table 2). See appendix 2 for more detail on fossil and trace fossil observations.]
Appendixes 41

Drilling depth 

interval

Description from drilling speed 

and onsite observations

Descriptions of mud stream samples Descriptions of core barrel samples

221–231 ft(67.4–70.4 m)(No core sample)

Mostly sand, with perhaps 

a little sandy clay. Geophysical logs show increased resistivity and density values for the interval 224–232 ft, suggesting some lithification

Bucket sample, 221–231 ft.

Coarse sand to silt with medium-sorted, subangular to 

rounded grains. A few small clumps of calcareous mud. Calcareous. Abundant ostracods; several were sampled.

N/A

231–241 ft(70.4–73.5 m)Core run 17

Sand with clay at 232.0–233.5 

ft and 237–241 ft. Clay has a bluish tint

Bucket sample, 231–241 ft (minimal material recovered).

Coarse to fine sand with medium- to well-sorted, subangular 

to rounded grains. Calcareous. Shell fragments. Some or all of the material may have come from a different depth interval.

Core, top 4.8 ft (7.3 ft total onsite recovery, divided). Top 

probably at 232 ft.

3.8–4.8 Clay with very little silt. Calcareous. Ostracods and 

unidentified, possible fossils. 

3.6–3.8 Silty clay. Calcareous. Ostracods and unidentified, 

possible fossils. 

0.0–3.6 Clay with very little silt. Calcareous. Possible 

bioturbation at 1.1 ft and indicated by centimetersize ovals with rust-colored haloes at 0.8 ft. Otherwise, no visible laminations throughout the interval. Gastropods and other shells. Carbon residue, woody plant fragments, and tooth or bone fragments at 0.2 ft.

Core, bottom 2.5 ft (7.3 ft total recovered, divided).

0.0–2.5 Silt to clay with massive clay from 0.0–0.3 ft. 

Calcareous. Possible bioturbation at 0.4 and 1.5 ft. Parallel lamina at 1.6 ft (faint) and at 2.0–2.5 ft. 

Vertebrate fragment at 1.7 ft, unidentified shell 

fragments at 0.4 to 0.8 ft. Sample taken at 1.2 ft for XRD analysis. 

Core catcher sample, probably from 241 ft.

Tan-colored, fine silt to clay with some mica. Slightly 

calcareous. 

241–251 ft(73.5–76.5 m)(No core sample)

Sand with clay at 243.0–244.0 

ft and 249.5–251 ft

Bucket sample, 241–251 ft (little material recovered).

Fine sand to silt with subangular to rounded grains. 

Noncalcareous. Magnetite grains. Shell fragments, glass bubble, ash shards. 

N/A

Appendix 1. Descriptions of samples by type and drilling interval.—Continued[Drilling depth interval, interval evaluated for sampling; those sampled for core are indicated by the core run number; depths listed in feet (ft), corresponding to drilling procedures; m, meters. Sample types described in text and table 1. N/A, not applicable. XRD, X-ray diffraction. Analyses are presented in appendix 3. Onsite core recovery length is the original length measured in 2009. Cores are logged from bottom (0.0 ft) to the top of the sample relative to core lengths measured in 2013, which could be different than the onsite length (table 2). See appendix 2 for more detail on fossil and trace fossil observations.]
42 Sample Descriptions and Geophysical Logs for Cored Well, Great Sand Dunes National Park, Colorado Drilling depth interval Description from drilling speed and onsite observations Descriptions of mud stream samples Descriptions of core barrel samples 251–261 ft (76.5–79.6 m) Core run 18 Sand 251–256 ft. Soft blue clay at 256–261 ft. Light-colored band 52–53 in. from top of core. Wide black bands between 35–39 in. from top of core. Sieve sample, 251–261 ft. Fine sand to clay. Calcareous. Volume of the sieve sample is much greater than that of the bucket sample. Bucket sample, 251–261 ft (little material recovered). Medium sand to silt with subangular to rounded grains. Clay chunks. Slightly calcareous. Some or all of the material may have come from a different depth interval. Core, top 4.8 ft (6.2 ft total onsite recovery, divided). 4.5–4.8 Silt to clay, grading upward from calcareous to more calcareous. At the bottom of this interval, a 0.1-ft- thick, olive-colored, silty clay layer is bounded above and below by two rust-colored laminations. Top of this core is probably at 256 ft depth. 3.9–4.5 Clay with faint, parallel laminations. Grades upward from noncalcareous to calcareous. 1.6–3.9 Clay with faint, parallel laminations. Noncalcareous. Possible burrow with rust-colored ring haloes at 1.8 ft. Possible burrows at 2.5 ft. Ostracods. 1.3–1.6 Clay with faint, parallel laminations. Calcareous. Ostracods. 0.5–1.3 Clay with faint, parallel laminations. Noncalcareous. Possible root trace at 0.7 ft. Possible burrow at 1.0 ft. Ostracods and other shells. 0.0–0.5 Clay with faint, parallel laminations. Calcareous. Core, bottom 1.4 ft (6.2 ft total recovered, divided). 0.0–1.4 Clay with faint parallel laminations. Calcareous. A couple of pebble-sized pieces of magnetite at 1.0 ft; samples collected. Ostracods and other possible fossils. Core catcher sample. Clay with faint laminations. Calcareous. Core piece, 0.7 ft long, recovered from subsequent run, probably from 261 ft. Fine sand to clay. Calcareous. Appendix 1. Descriptions of samples by type and drilling interval.—Continued [Drilling depth interval, interval evaluated for sampling; those sampled for core are indicated by the core run number; depths listed in feet (ft), corresponding to drilling procedures; m, meters. Sample types described in text and table 1. N/A, not applicable. XRD, X-ray diffraction. Analyses are presented in appendix 3. Onsite core recovery length is the original length measured in 2009. Cores are logged from bot- tom (0.0 ft) to the top of the sample relative to core lengths measured in 2013, which could be different than the onsite length (table 2). See appendix 2 for more detail on fossil and trace fossil observations.]
Appendixes 43

Drilling depth 

interval

Description from drilling speed 

and onsite observations

Descriptions of mud stream samples Descriptions of core barrel samples

261–266 ft(79.6–81.1 m)Core run 19

Blue-gray clay Bucket sample, 261–266 ft (minimal material recovered).

Fine sand to silt with medium-sorted, subangular to rounded 

grains. Noncalcareous. A few ash shards. Some or all of the material may have come from a different depth interval.

Core (4.5 ft onsite recovery), top probably from 261 ft.

3.6–4.0 Gradual increase upward from clay to silt. Very 

calcareous. Parallel laminations. Ostracods in siltier interval. 

1.6–3.6 Silt to clay, very little silt. Very calcareous. Parallel 

laminations. Slickenside measured 40o from parallel to core, opposite orientation to the one below. Ostracods and other shells. Diatoms at 2.8 ft. 

0.0–1.6 Clay. Very calcareous. Parallel laminations. 

Slickenside measured 40o from parallel to core, opposite orientation to the one above. Ostracods.

Core catcher sample.

Fine sand to clay, mostly clay. Gypsum crystals. Calcareous. 

Abundant ostracods.

266–271 ft(81.1–82.6 m)Core run 20

Blue-gray clay. Bucket sample, 266–271 ft (minimal material recovered).

Fine sand to silt with medium-sorted, subangular to 

rounded grains, some or all of which may have come from a different depth interval. Slightly calcareous. Clumps of clay. Ostracods.

Core (3.8 ft onsite recovery).

3.1–3.5 Massive clay. Calcareous. Ostracods.3.0–3.1 Silty clay. Calcareous. Ostracods. 1.7–3.0 Massive clay with 1-inch-thick ostracod bed at 

about 2.5 ft. Calcareous. 

1.6–1.7 Silt to clay, mostly clay. Calcareous. Ostracods.1.3–1.6 Clay. Calcareous. Ostracods. 1.0–1.3 Silt to clay, mostly clay. Calcareous. Ostracods. 0.5–1.0 Clay with ostracod coquina at about 0.9 ft. Faint 

laminations. Calcareous. 

0.2–0.5 Silt to clay, mostly clay. Calcareous. 0.0–0.2 Clay with ostracods. Calcareous. 

Core catcher sample.

Clay with very little silt. Calcareous. Ostracods.

271–276 ft(82.6–84.1 m)Core run 21

Blue-gray clay. Much of the 

core was deformed from drilling.

Bucket sample, 271–276 ft (minimal material recovered).

Fine sand to clay with clay chunks. Calcareous. Some or 

all of the material may have come from a different depth interval.

Core (3.7 ft onsite recovery; core was deformed from drilling).

0.0–3.2 Massive blue clay with very little silt. Calcareous. 

Sample taken for XRD analysis at 1 ft. Difficult to tell, but appears to have no sedimentary structures or trace fossils. Ostracods are present throughout, especially abundant at about 1.4 ft. 

Core catcher sample, probably from 274–275 ft, based on logs.

Clay with some dark fine sand grains. Abundant gypsum 

crystals, some mica. Calcareous. Ostracods.

Appendix 1. Descriptions of samples by type and drilling interval.—Continued[Drilling depth interval, interval evaluated for sampling; those sampled for core are indicated by the core run number; depths listed in feet (ft), corresponding to drilling procedures; m, meters. Sample types described in text and table 1. N/A, not applicable. XRD, X-ray diffraction. Analyses are presented in appendix 3. Onsite core recovery length is the original length measured in 2009. Cores are logged from bottom (0.0 ft) to the top of the sample relative to core lengths measured in 2013, which could be different than the onsite length (table 2). See appendix 2 for more detail on fossil and trace fossil observations.]
44 Sample Descriptions and Geophysical Logs for Cored Well, Great Sand Dunes National Park, Colorado Drilling depth interval Description from drilling speed and onsite observations Descriptions of mud stream samples Descriptions of core barrel samples 276–291 ft (84.1–88.7 m) Core run 22 Mostly sand with some clay layers Bucket sample, 276–281 ft. Fine sand to silt with medium-sorted, subangular to rounded grains. Very slightly calcareous. Bucket sample, 281–291 ft. Fine sand to silt with medium-sorted, subangular to rounded grains. Very slightly calcareous. Some clay balls, ostracods, and a few ash shards. Viscous fluid sample, scooped. Fine sand to silt with medium-sorted, subangular to rounded grains. Noncalcareous. Core (0.9 ft onsite recovery, probably from about 280 ft, based on logs). 0.0–0.8 Silty, blue clay. Fine, wavy to parallel laminations in upper 0.6 ft; lower 0.3 ft very massive. Calcareous throughout. Ostracods. Core was coated in sand. Sample collected at 0.2 ft for XRD analysis. Core catcher sample. Clay with some fine sand. Mica, ostracods. Calcareous. 291–301 ft (88.7–91.7 m) Core run 23 Sand with gray clay below 295 ft Bucket sample, 291–301 ft. Fine sand to silt with subangular to rounded grains. Very slightly calcareous Core piece, 0.4 ft long, from top of core, probably from 295 ft. Greenish-gray clay with some fine sand interbeds. Dark patches. Disrupted interbeds with rip-up clasts(?). Breccia from a slump or debris flow. Calcareous. Shell fragments. Core (4.9 ft onsite recovery, probably from 295–300 ft). 4.0–5.0 Abrupt change in color above 4.0 ft to dark gray, silty clay with a thin layer of lighter color clay at 4.3 ft. Grades to clay in the top 0.3 ft of the interval. Very bioturbated below 4.2 ft, with parallel laminations from 4.4 to 4.8 ft and wavy laminations above that. Ostracods and abundant shell fragments. Calcareous throughout. 0.0–4.0 Tan clay with very little silt. Very bioturbated except for a 0.1-ft- thick zone of faint laminations at 1 ft. Burrows, gastropods, and other shell fragments within the interval. Root traces at 2.7 ft. Calcareous throughout. Abrupt change in color above 4.0 ft. Core catcher sample. Massive gray clay, calcareous. Sample collected for XRD analysis Appendix 1. Descriptions of samples by type and drilling interval.—Continued [Drilling depth interval, interval evaluated for sampling; those sampled for core are indicated by the core run number; depths listed in feet (ft), corresponding to drilling procedures; m, meters. Sample types described in text and table 1. N/A, not applicable. XRD, X-ray diffraction. Analyses are presented in appendix 3. Onsite core recovery length is the original length measured in 2009. Cores are logged from bot- tom (0.0 ft) to the top of the sample relative to core lengths measured in 2013, which could be different than the onsite length (table 2). See appendix 2 for more detail on fossil and trace fossil observations.]
Appendixes 45

Drilling depth 

interval

Description from drilling speed 

and onsite observations

Descriptions of mud stream samples Descriptions of core barrel samples

301–306 ft(91.7–93.3 m)Core run 24

Gray clay Bucket sample, 301–306 ft (minimal material recovered).

Fine sand to silt with subangular to rounded grains, some or 

all of which may have come from a different depth interval. Mud clumps 

Core (5 ft onsite recovery).

0.0–5.0 Massive gray clay with very little silt and some 

mica. Faint laminations at the bottom 2 ft or so, with faint light and dark laminations, root trace, and other evidence of bioturbation at the bottom 0.1 ft. Ostracod at 2.4 ft; possible bone fragments at 2.9 ft. Otherwise, almost no sedimentary structures, shells, burrows, and so forth; possibly completely bioturbated. Noncalcareous from 0–4.2 ft; calcareous above that. Sample taken from 1.7 ft for XRD analysis. Sample taken from 0.2 ft was examined for diatoms but none were found. Deformation caused by drilling from 3.8–4.2 ft.

306–311 ft(93.3–94.8 m)Core run 25

Consolidated gray clay. 

Field photos show angular laminations and dark gray or greenish, oval or round spots of about 1-2 inches in diameter in the top 1 foot of the core recovered. 

Bucket sample, 306–311 ft (minimal material recovered).

Fine sand to silt with subangular to rounded grains, some or 

all of which may have come from a different depth interval. Mud clumps 

Core (2 ft onsite recovery).

0.0–1.9 Gray clay with some silt and some mica. No 

bioturbation or shells. Massive for the bottom 0.2 ft; abrupt transition to parallel laminations above 0.2 ft. Noncalcareous throughout. 

Core catcher sample.

Silt to clay, very calcareous. Faintly laminated.

311–316 ft(94.8–96.3 m)Core run 26

Sandy clay or a few stringers 

of sand within mostly gray clay. A 1.5-inch light-tan band occurs about 3.5 ft from bottom of core.

Bucket sample, 311–316 ft (minimal material recovered).

Fine sand to silt with subangular to rounded grains, some or 

all of which may have come from a different depth interval. Mud clumps 

Core piece, 0.2 ft from top of core.

Clay with some fine sand grains. Noncalcareous. 

Core (4.8 ft onsite recovery).

0.0–4.5 Gray clay with some silt and some mica. No 

bioturbation or shells, but may contain organic remains. Parallel laminations throughout. Noncalcareous throughout. A 1.5-inch light-rustcolored, laminated band occurs at about 3.2 ft and exhibits less shrinkage than the rest of the core. XRD analyses of samples from the band at 3.2 ft and above the band at 3.8 ft show high magnesium calcite in the band and low magnesium calcite outside of the band.

Appendix 1. Descriptions of samples by type and drilling interval.—Continued[Drilling depth interval, interval evaluated for sampling; those sampled for core are indicated by the core run number; depths listed in feet (ft), corresponding to drilling procedures; m, meters. Sample types described in text and table 1. N/A, not applicable. XRD, X-ray diffraction. Analyses are presented in appendix 3. Onsite core recovery length is the original length measured in 2009. Cores are logged from bottom (0.0 ft) to the top of the sample relative to core lengths measured in 2013, which could be different than the onsite length (table 2). See appendix 2 for more detail on fossil and trace fossil observations.]
46 Sample Descriptions and Geophysical Logs for Cored Well, Great Sand Dunes National Park, Colorado Appendix 1. Descriptions of samples by type and drilling interval.—Continued [Drilling depth interval, interval evaluated for sampling; those sampled for core are indicated by the core run number; depths listed in feet (ft), corresponding to drilling procedures; m, meters. Sample types described in text and table 1. N/A, not applicable. XRD, X-ray diffraction. Analyses are presented in appendix 3. Onsite core recovery length is the original length measured in 2009. Cores are logged from bot- tom (0.0 ft) to the top of the sample relative to core lengths measured in 2013, which could be different than the onsite length (table 2). See appendix 2 for more detail on fossil and trace fossil observations.] Drilling depth interval Description from drilling speed and onsite observations Descriptions of mud stream samples Descriptions of core barrel samples 316–321 ft (96.3–97.8 m) Core run 27 Gray clay with a coarser grained layer about 1.5 ft from the top of the core. Bucket sample, 316–321 ft (minimal material recovered). Fine sand to silt with subangular to rounded grains, some or all of which may have come from a different depth interval. Mud clumps Core (5 ft onsite recovery). 0.0–4.5 Gray clay with very little silt and some mica. Noncalcareous throughout. Parallel laminations throughout. The bottom 2.8 ft consists of many light-colored laminations about 2 millimeters thick; no pattern is observed. A few ostracods and other shells observed within 2.5–4.4 ft. A thin bed of bivalves and possible gastropods at 3.1 ft is surrounded by light-rust-colored sediment. Possible light-rust-colored oval burrow at 4.4 ft. Sample taken from 0.7 ft was examined for diatoms but none were found. Core piece, 0.1 ft from bottom of core. Clay with some fine sand grains. Noncalcareous. 321–326 ft (97.8–99.4 m) Core run 28 Gray clay. The top 2.7 ft of the core was deformed from drilling Bucket sample, 321–326 ft (minimal material recovered). Fine sand to silt with subangular to rounded grains, some or all of which may have come from a different depth interval. Ostracods and gastropod fragments Core (4.6 ft onsite recovery). 0.0–4.3 Gray clay with some silt and less mica than above. Slightly calcareous. No sand interbeds. No laminations visible, but difficult to tell because the core was deformed by drilling from 1.6 to 4.3 ft. A light-rust-colored bed at 2.5 ft is very calcareous. Sample taken for XRD analysis at 2.7 ft. Core catcher sample. Silt to clay with light and dark laminations. Noncalcareous.
Appendixes 47

Appendix 2. Depth intervals where fossils or other evidence of life were observed.[Observations and identifications were made in 2012 by M.E. Benson and J.K. Davis, in 2013 by G. Skipp, and in 2014 by M.E. Benson. Refer to appendix 1 for detailed descriptions of samples and figure 7 for positions of core samples within the well. Measurements in inches (in); centimeters (cm); millimeters (mm); feet (ft); meters (m). N/A, not applicable]

Drilling depth 

interval Sample type Year of observation* Measured length of core sample* Distance measured from bottom of core sample* Observation(s) Comments

70–80 ft(21.3–24.4 m)Core run 2

Core catcher 2014 N/A N/A Diatoms One small sample of gray silty clay was examined 

by M.E. Benson and found to contain a lowdiversity diatom assemblage consisting of centric diatoms of the tentatively identified centric diatom species Aulacoseira distans, and Stephanodiscus sp., as well as possibly other genera in the Stephanodiscaceae family.

131–141 ft(39.9–43.0 m)Core run 11

Core 2013 10.0 in

(25.4 cm)

8–10 in(20–25 cm)

Possible bioturbation 

171–191 ft(52.1–58.2 m)Core run 13

Core 2012 47.2 in

(120.0 cm)

20–24 in(50–60 cm)

Ostracods A few ostracods observed.

181–191 ft(55.2–58.2 m)

Bucket sample 2013 N/A N/A Clam shells Very tiny shells collected.

191–201 ft(58.2–61.3 m)Core run 14

Core 2013 37.0 in

(94.0 cm)

28 in(71 cm)

Shell Single unidentified shell observed.

Core catcher 2013 N/A N/A Bivalve shell Tiny shell collected.

201–211 ft(61.3–64.3 m)Core run 15

Core 2013 20.0 in

(50.8 cm)

12 in(30 cm)

Shell fragment Single unidentified shell fragment observed.

211–221 ft(64.3–67.4 m)Core run 16

Core 2012 24.8 in

(63.0 cm)

17–25 in(43–63 cm)

Ostracods, clam, shell 

fragments

Whole ostracod and unidentified shell fragments 

collected 19 in (48 cm) above the bottom of the core.

2013 26.0 in

(66.0 cm)

23 in(58 cm)

Shell fragments Unidentified shell fragments observed.

Core catcher 2013 N/A N/A Bivalve fragments, 

fish bones?

Bones (possible fish bones) collected. 

221–231 ft(67.4–70.4 m)

Bucket sample 2013 N/A N/A Ostracods Abundant ostracods; several collected.

*Measured lengths of core samples and distances relative to their bottoms are listed by year because measurements varied by year of observation (see table 2).
48 Sample Descriptions and Geophysical Logs for Cored Well, Great Sand Dunes National Park, Colorado Drilling depth interval Sample type Year of observation* Measured length of core sample* Distance measured from bottom of core sample* Observation(s) Comments 231–241 ft (70.4–73.5 m) Core run 17 Core (top piece) 2012 55.9 in (142.0 cm) 52 in (132 cm) Ostracods 46 in (118 cm) Fossil Unidentified fossil collected. 36–56 in (92–142 cm) Ostracod, unknown white circular grains Unknown fine white circular grains may or may not be fossils. 34 in (86 cm) Possible gastropod Possible gastropod collected. 33–35 in (84–89 cm) Shell fragments Unidentified shell fragments collected. 32–36 in (82–92 cm) Gastropods A few gastropods were observed. 13 in (32 cm) Gastropods, bioturbation 9 in (24 cm) Burrow Burrow sampled. 5 in (12 cm) Possible black shells Black-colored specimens that may be shells were collected. 4–13 in (9–32 cm) Gastropod, unknown white circular grains Unknown fine white circular grains may or may not be fossils. 2 in (4 cm) Carbon residue, woody plant fragments, tooth or bone fragments 2013 57.5 in (146.1 cm) 10 in (25 cm) Possible bioturbation Possible bioturbation indicated by 1-cm-size ovals with rust-colored haloes. Appendix 2. Depth intervals where fossils or other evidence of life were observed.—Continued [Observations and identifications were made in 2012 by M.E. Benson and J.K. Davis, in 2013 by G. Skipp, and in 2014 by M.E. Benson. Refer to appendix 1 for detailed descriptions of samples and figure 7 for positions of core samples within the well. Measurements in inches (in); centimeters (cm); millimeters (mm); feet (ft); meters (m). N/A, not applicable] *Measured lengths of core samples and distances relative to their bottoms are listed by year because measurements varied by year of observation (see table 2).
Appendixes 49

Drilling depth 

interval Sample type Year of observation* Measured length of core sample* Distance measured from bottom of core sample* Observation(s) Comments

231–241 ft(70.4–73.5 m)Core run 17

Core (bottom 

piece)

2012 28.3 in

(72.0 cm)

20 in(50 cm)

Vertebrate fossil Fragments of vertebrate remains collected. 

7 in(18 cm)

Shell fragments Unidentified shell fragments collected. 

5–9 in(12–22 cm)

Shell fragments Unidentified shell fragments. 

2013 29.4 in

(74.7 cm)

18 in(46 cm)

Possible bioturbation

5 in(12 cm)

Possible bioturbation

241–251 ft(73.5–76.5 m)

Bucket sample 2013 N/A N/A Shell fragments Unidentified shell fragments observed.

251–261 ft(76.5–79.6 m)Core run 18

Core (top 

piece)

2012 51.6 in

(131.0 cm)

33 in(83 cm)

Ostracods

13 in(32–34 cm)

Shell fragments Unidentified shell fragments were collected. 

0–20 in(1–51 cm)

Ostracods Ostracods were observed throughout this interval.

2013 57.5 in

(146.1 cm)

30 in(76 cm)

Burrows Possible burrows. 

22 in(55 cm)

Burrow Possible burrow indicated by rust-colored haloes. 

12 in(30 cm)

Burrow Possible burrow. 

8 in(20 cm)

Root trace Possible root trace. 

Core (bottom 

piece)

2012 13.8 in

(35.0 cm)

0–14 in(0–35 cm)

Ostracods, unknown 

circular white grains, shell fragments

Ostracods and unknown fine white circular grains, 

which may or may not be fossils, were observed throughout the core piece. Unidentified shell fragments were collected 3 in (7 cm) above the bottom of the core piece. 

Appendix 2. Depth intervals where fossils or other evidence of life were observed.—Continued[Observations and identifications were made in 2012 by M.E. Benson and J.K. Davis, in 2013 by G. Skipp, and in 2014 by M.E. Benson. Refer to appendix 1 for detailed descriptions of samples and figure 7 for positions of core samples within the well. Measurements in inches (in); centimeters (cm); millimeters (mm); feet (ft); meters (m). N/A, not applicable]

*Measured lengths of core samples and distances relative to their bottoms are listed by year because measurements varied by year of observation (see table 2).
50 Sample Descriptions and Geophysical Logs for Cored Well, Great Sand Dunes National Park, Colorado Drilling depth interval Sample type Year of observation* Measured length of core sample* Distance measured from bottom of core sample* Observation(s) Comments 261–266 ft (79.6–81.1 m) Core run 19 Core 2012 45.7 in (116.0 cm) 0–46 in (0–116 cm) Ostracods Ostracods abundant throughout this core sample, especially at 4 in (10 cm) above the bottom of the sample. Samples collected at 17 in (43 cm) and 36 in (91 cm) above the bottom of the sample. 34 in (86 cm) Diatoms, ostracods A few diatoms were present in a sample containing ostracods. M.E. Benson observed a low- diversity diatom assemblage dominated by the tentatively identified small centric species Aulacoseira distans and the large pennate species Anomoeoneis sphaerophora f. costata. Additional pennate genera, possibly of the Achnanthidiaceae and Fragilariaceae families, as well as one specimen resembling the genus Surirella, were also observed. 22–30 in (56–76 cm) Shell fragments Unknown shell fragments. 2013 48.0 in (121.9 cm) 44–46 in (112–116 cm) Ostracods Abundant ostracods observed within a silty interval. Core catcher 2013 N/A N/A Ostracods Abundant ostracods throughout the sample. 266–271 ft (81.1–82.6 m) Core run 20 Core 2012 39.4 in (100.0 cm) 0–39 in (0–100 cm) Ostracods Ostracods abundant throughout the sample, with ostracod coquinas at 10–11 in (25–28 cm), 25–26 in (64–65 cm), and 30 in (75 cm) above the bottom. Shell fragments and ostracods collected from the lower two coquinas. 35 in (90 cm) Unknown specimen An unidentified specimen of brown color was collected. 2013 42.0 in (106.7 cm) 30 in (76 cm) Ostracods Ostracod coquina about 1 in (3 cm) thick. 12 in (30 cm) Ostracods

2 in(6 cm)

Ostracods

Core catcher 2013 N/A N/A OstracodsBucket sample 2013 N/A N/A Ostracods

Appendix 2. Depth intervals where fossils or other evidence of life were observed.—Continued[Observations and identifications were made in 2012 by M.E. Benson and J.K. Davis, in 2013 by G. Skipp, and in 2014 by M.E. Benson. Refer to appendix 1 for detailed descriptions of samples and figure 7 for positions of core samples within the well. Measurements in inches (in); centimeters (cm); millimeters (mm); feet (ft); meters (m). N/A, not applicable]

*Measured lengths of core samples and distances relative to their bottoms are listed by year because measurements varied by year of observation (see table 2).
Appendixes 51

Drilling depth 

interval Sample type Year of observation* Measured length of core sample* Distance measured from bottom of core sample* Observation(s) Comments

271–276 ft(82.6–84.1 m)Core run 21

Core 2012 35.4 in

(90.0 cm)

0–35 in(0–90 cm)

Ostracods Ostracods observed throughout the core sample. 

They are abundant 16–17 in (41–42 cm) above the base of the sample. Specimens collected from 17 in (42 cm) and 1 in (3 cm) above the bottom of the core sample. 

Core catcher 2013 N/A N/A Ostracods

276–291 ft(84.1–88.7 m)Core run 22

Core 2012 9.1 in

(23.0 cm)

0–9 in(0–23 cm) 

Ostracods Ostracods observed throughout the whole sample. 

Specimens collected 7 in (17 cm) above the bottom of the core sample. 

Core catcher 2013 N/A N/A Ostracods

291–301 ft(88.7–91.7 m)Core run 23

Core piece at 

top

2013 N/A N/A Shell fragments Unidentified shell fragments observed.

Core 2012 57.9 in

(147.0 cm)

50–58 in(127–147 cm)

Ostracods, shell 

fragments

Ostracods and unknown 5-mm-size shell fragments 

observed. J.K. Davis collected samples of ostracods and other fossils from 53 in (135 cm) and 54–55 in (137–140 cm). 

42–46 in(107–117 cm)

Gastropods, shell 

fragments

Gastropods and unknown 5-mm-size shell 

fragments observed.

30–42 in(77–107 cm)

Shell fragments A few unknown, 2-mm-size shell fragments 

observed.

32 in(81 cm)

Bioturbation, root 

traces, gastropods

Bioturbation, possible root traces, and fragments of 

gastropods observed. 

19–26 in(47–67 cm)

Shell fragments Unknown 1-mm-size shell fragments observed.

2013 60.0 in

(152.4 cm)

0–50 in(0–128 cm)

Bioturbation, burrows, 

shell fragments

Sample shows intense bioturbation, with burrows 

at 18 in (46 cm), 19 in (49 cm), 24 in (61 cm), 30 in (76 cm), and possibly at 2 in (6 cm) above bottom of the core, respectively. Shell fragments were also observed at 24 in (61 cm). 

48–58 in(122–147 cm)

Shell fragments Abundant shell fragments.

17 in(43 cm)

Gastropod A small gastropod observed.

Appendix 2. Depth intervals where fossils or other evidence of life were observed.—Continued[Observations and identifications were made in 2012 by M.E. Benson and J.K. Davis, in 2013 by G. Skipp, and in 2014 by M.E. Benson. Refer to appendix 1 for detailed descriptions of samples and figure 7 for positions of core samples within the well. Measurements in inches (in); centimeters (cm); millimeters (mm); feet (ft); meters (m). N/A, not applicable]

*Measured lengths of core samples and distances relative to their bottoms are listed by year because measurements varied by year of observation (see table 2).
52 Sample Descriptions and Geophysical Logs for Cored Well, Great Sand Dunes National Park, Colorado Drilling depth interval Sample type Year of observation* Measured length of core sample* Distance measured from bottom of core sample* Observation(s) Comments 301–306 ft (91.7–93.3 m) Core run 24 Core 2012 56.3 in (143.0 cm) 2 in (5 cm) Bioturbation, root traces Root traces and other bioturbation features were observed. M.E. Benson examined the sample for diatoms and found none. 2013 60.0 in (152.4 cm) 35 in (85 cm) Possible bone fragments 29 in (73 cm) Ostracod 316–321 ft (96.3–97.8 m) Core run 27 Core 2012 53.1 in (135.0 cm) 49–53 in (125–135 cm) Shell fragments A few, unidentified 1-mm-size shell fragments observed. 37–49 in (95–125 cm) Ostracods A few ostracods observed. 37 in (95 cm) Gastropods, bivalves Horizon of abundant gastropods and bivalves (possible clams). Samples collected. 30–37 in (75–95 cm) Ostracods A few ostracods observed. 8 in (21 cm) M.E. Benson examined a sample for diatoms within a white-colored band but found none. 2013 54.0 in (137.2 cm) 53 in (137 cm) Burrow Possible burrow indicated by a rust-colored oval. 37 in (95 cm) Bivalves, burrow Horizon of abundant bivalves. Possible burrow surrounded by light rust-colored sediment. 321–326 ft (97.8–99.4 m) Bucket sample 2013 N/A N/A Ostracods and gastropods Ostracods and gastropod fragments were observed in this sample, but may have come from a higher interval within the well. *Measured lengths of core samples and distances relative to their bottoms are listed by year because measurements varied by year of observation (see table 2). Appendix 2. Depth intervals where fossils or other evidence of life were observed.—Continued [Observations and identifications were made in 2012 by M.E. Benson and J.K. Davis, in 2013 by G. Skipp, and in 2014 by M.E. Benson. Refer to appendix 1 for detailed descriptions of samples and figure 7 for positions of core samples within the well. Measurements in inches (in); centimeters (cm); millimeters (mm); feet (ft); meters (m). N/A, not applicable]
Appendixes 53

Appendix 3. Results of analysis by X-ray powder diffraction 

[Depth in feet (ft); meters (m); in., inch. Refer to appendix 1 for detailed descriptions of samples. Minerals are listed in order of peak X-ray intensity]

Drilling interval Sample type Description of specimen collected Bulk X-ray minerology

30–40 ft

(9.1–12.2 m)

Hopper, fine fraction Fine sand Quartz, anorthite, albite, cristobalite, 

potassium feldspar, amphibole, mica.

70–80 ft

(21.3–24.4 m)

Core catcher Clay from about 77 ft depth Quartz, plagioclase feldspar, calcite, 

cristobalite, clay, mica.

70–80 ft

(21.3–24.4 m)

Core catcher Silt from about 77 ft depth Quartz, plagioclase feldspar, cristobalite, 

calcite, clay, mica. 

80–90 ft

(24.4–27.4 m)

Core catcher Very fine sand to clay, possibly from about 

85 ft depth

Quartz, albite, cristobalite, potassium 

feldspar, mica, smectite.

119–125 ft

(36.3–38.1 m)

Core catcher Fine sand to silt, probably from somewhere 

between 121 and 125 ft depth

Quartz, plagioclase feldspar, cristobalite, 

potassium feldspar, clay, pyrite?

191–201 ft

(58.2–61.3 m)

Core Silty clay taken from approximately 2 ft 

above the bottom of the core

Quartz, plagioclase feldspar, cristobalite, 

potassium feldspar, clay.

191–201 ft

(58.2–61.3 m)

Core Very fine sand taken from the lower foot of 

the core

Cristobalite, quartz, plagioclase feldspar, 

mica.

231–241 ft

(70.4–73.5 m)

Core Clay taken from 14 in. above the bottom of 

the bottom core piece, probably at about 

239–240 ft depth

Quartz, plagioclase feldspar, cristobalite, 

calcite, clay, mica, kaolinite. 

271–276 ft

(82.6–84.1 m)

Core Clay taken from 11 in. above the bottom of 

the core, at about 273 ft depth

Quartz, calcite, plagioclase feldspar, 

cristobalite, potassium feldspar, clay, mica.

276–291 ft

(84.1–88.7 m)

Core Clay taken from 2 in. above the bottom of 

the core, probably at about 280 ft depth

Quartz, calcite, plagioclase feldspar, 

cristobalite, clay, potassium feldspar, mica, 

kaolinite.

291–301 ft

(88.7–91.7 m)

Core catcher Clay from about 300 ft depth Quartz, calcite, plagioclase feldspar, 

cristobalite, clay, potassium feldspar, mica, 

kaolinite.

301–306 ft

(91.7–93.3 m)

Core Clay taken from 20 in. above the bottom of 

the core, at about 304 ft depth

Plagioclase feldspar, quartz, cristobalite, 

dolomite, potassium feldspar, clay, mica, 

kaolinite.

311–316 ft

(94.8–96.3 m)

Core Clay taken at 45 in. from the bottom of the 

core, sampled above a light-rust-colored 

band at 38 in. Sample probably from a 

depth of about 312 ft

Cristobalite, plagioclase feldspar, quartz, 

potassium feldspar, calcite, clay, kaolinite, 

mica.

311–316 ft

(94.8–96.3 m)

Core Sample taken from a light-rust-colored, 

laminated band 38 in. above the bottom of 

the core, probably at about 313 ft depth

High-magnesium calcite, plagioclase 

feldspar, cristobalite, quartz, potassium 

feldspar, clay, mica. 

321–326 ft

(97.8–99.4 m)

Core Clay taken from 32 in. above the bottom of 

the core, at about 322 ft depth

Quartz, plagioclase feldspar, cristobalite, 

potassium feldspar, clay, calcite, kaolinite, 

mica.
Publishing support provided by the U.S. Geological Survey Science 

Publishing Network, Rolla Publishing Service Center and 

Denver Publishing Service Center

For more information concerning the research in this report, contact the 

Director, Crustal Geophysics and Geochemistry Science Center 

U.S. Geological Survey 

Box 25046, Mail Stop 964 

Denver, CO 80225 

http://crustal.usgs.gov/

Grauch and others— Sample Descriptions and Geophysical Logs for Cored Well, Great Sand Dunes National Park, Colorado—Data Series 918

ISSN 2327-638X (online)

http://dx.doi.org/10.3133/ds918