Quick Reference Guide for Users

This User’s Guide describes metadata for Data Series 

906, Preliminary Geologic Map of the Mount Hood 30- 

by 60-Minute Quadrangle, Northern Cascade Range, 

Oregon. The guide is intended to be a quick reference 

that augments the conventional metadata text document 

(filename: Metadata_MH_20141218, as txt or html). Tables 

here present the key information needed to assemble the 

map for viewing. Explanations in this document may also 

prove helpful for understanding decisions made during the 

compilation of the geologic map.

Projection and Datum

All GIS datasets are stored in the Oregon Lambert 

(Lambert conformal conic) projection, North American 

1983 datum (table 1). The corresponding EPSG code is 

2992 (http://http://spatialreference.org/ref/epsg/2992/). 

Point data are provided in spreadsheet format with 

geographic coordinates in degrees of longitude and latitude, 

NAD83.

Files and File Structure

This data series comprises 11 data layers necessary 

to assemble the geologic map (table 2). Discussion here 

addresses those that have greater complexity or require 

look-up tables. The datasets are enumerated fully in 

the standard metadata document (filename Metadata_

MH_20141218).

Coding for Stratigraphic Units (MH_Geopoly)

Map units are given a map-unit mnemonic in the 

columnar data (table 3), in order to label polygons 

according to age and formation or lithology (for example, 

Qal, Quaternary alluvium). Each map unit also has an 

integer value for stratigraphic coding (strat_code) in the 

shape file attribute table, for users who prefer identifying 

units by numeric values. Full unit names in the shape 

file match those in the Description of Map Units that 

accompanied the 1995 publication. The map-unit symbol is 

that used on the printed or image version of the map.

Coding for Map-Unit Contacts (MH_Contacts)

Given the reconnaissance nature of our mapping, 

most contacts can be shown uniformly, such as by solid 

line, with accuracy defined as “precisely or approximately 

located” (table 4). A few contacts, described as inferred 

and shown by short-dashed lines on the map, are drawn 

chiefly on the basis of geomorphology. Shown dotted are 

internal contacts that allow visual subdivision (on the map) 

according to successively younger age of some deposits 

emplaced during the Polallie eruptive period on Mount 

Hood.

A figurative contact, as hachured line, bounds an area 

in the Salmon Creek drainage. The area is poorly mapped 

owing to thick vegetation, poor exposure, and limited time 

for the reconnaissance mapping effort. Strata within the 

poorly mapped area are middle and possibly upper Miocene 

andesite lava flows, tuff breccia, and shallow intrusive 

rocks.

Also within the Contacts layer are lines corresponding 

to moraine crests. These lines trace geomorphic features, 

not boundaries of stratigraphic units.

Coding for Structural Features (MH_Structure)

Faults are the common structural feature in the map 

area, and they are coded by integer value such as 21, 22, 

or 24, with matching descriptions to indicate accuracy of 

Table 1. Projection and datum.

Element Definition

Projection:

Grid coordinate system

UTM zone number

Unit

1st standard parallel

2nd standard parallel

Central meridian

Latitude of projection’s origin

False Easting

False Northing

Horizontal datum name

Vertical datum

Ellipsoid name

EPSG code

Lambert conformal conic

Oregon Lambert projection

10

International foot (0.3048 m)

43

45.5

-120.5

41.75

1,312,335.958 ft (400,000 m)

0

North American datum 1983

NAVD 1988

GRS 1980

2992

Table 2. Files used to produce GIS version of geologic 

map.

Filename File Format

1 MH_Geopoly ESRI shp and Mapinfo TAB

2 MH_Patterns ESRI shp and Mapinfo TAB

3 MH_Contacts ESRI shp and Mapinfo TAB

4 MH_Structure ESRI shp and Mapinfo TAB

5 MH_Dikes ESRI shp and Mapinfo TAB

6 MH_Strikedip MS xls

7 MH_Ventsymbols MS xls

8 MH_Drillholes MS xls

9 MH_Magpolarity MS xls

10 MH_KARages MS xls

11 MH_Geogrnames MS xls
Table 3. Numeric code values and map-unit symbols and names for stratigraphic units. Table is also included as a 

separate file in the folder of spreadsheets for this publication.

 Label Code Name Age

 ow 1 Open water Holocene

 g 2 Glacier Holocene and Pleistocene

 Qabl 252 Andesite of Boulder Lake Pleistocene

Qac 302 Andesite of Cabin Creek Pleistocene

Qacl 308 Andesite west of Clear Lake Pleistocene

 Qae 224 Andesite of Enola Hill Pleistocene

 Qah 233 Andesite of Hiyu Mountain Pleistocene

 Qahr 221 Andesite of Horseshoe Ridge Pleistocene

 Qal 31 Alluvium Holocene and Pleistocene

 Qall 226 Andesite of Laurance Lake Pleistocene

 Qam 251 Andesite of McCubbins Gulch Pleistocene

 Qap 222 Andesite of Perry Lake Pleistocene

 Qas 303 Andesite of Skyline Road Pleistocene

 Qaw 306 Andesite of Wapinitia Pass Pleistocene

Qbaa 202 Basaltic andesite of Aschoff Buttes Pleistocene

Qbac 206 Basaltic andesite of Cloud Cap Pleistocene

 Qbac? 207 Basaltic andesite of Cloud Cap Pleistocene

Qbal 203 Basaltic andesite of Lost Lake Butte Pleistocene

 Qbap 205 Basaltic andesite of The Pinnacle Pleistocene

Qbas 204 Basaltic andesite of Stump Creek Pleistocene

 Qbc 208 Basalt of Crutcher Bench Pleistocene

Qbdc 209 Basaltic andesite of Devil Canyon Pleistocene

Qbdr 241 Basaltic andesite of Dog River Pleistocene

 Qbp 201 Basaltic andesite of Parkdale Holocene

 Qbr 223 Basaltic andesite of Blue Ridge Pleistocene

Qca 32 Colluvial and alluvial slope deposits Holocene and Pleistocene

 Qdf 307 Dacite of Frog Lake Buttes Pleistocene

 Qg 41 Glacial deposits Holocene and Pleistocene

 Qget 43 Glacial deposits, till of Evans Creek age Pleistocene

Qgnt 42 Glacial deposits, till of neoglacial age Holocene

Qha 133 Pre-Polallie rocks of Mount Hood, andesite and dacite lava Pleistocene 

Qhc 131 Pre-Polallie rocks of Mount Hood, pyroclastic-flow and debris-flow deposits Pleistocene 

Qhc? 132 Pre-Polallie rocks of Mount Hood, pyroclastic-flow and debris-flow deposits Pleistocene 

 Qhdl 111 Debris-avalanche deposit of Ladd Creek Holocene

Qhoc 102 Old Maid eruptive period, pyroclastic-flow and debris-flow deposits Holocene 

 Qhol 101 Old Maid eruptive period, lava flows Holocene

Qhpc 122 Polallie eruptive period, pyroclastic-flow and debris-flow deposits Pleistocene 

 Qhpl 121 Polallie eruptive period, lava Pleistocene

Qhtc 108 Timberline eruptive period, pyroclastic-flow and debris-flow deposits Holocene 

Qiba 62 Intrusive basalt and basaltic andesite Pleistocene

 Qls 34 Landslide deposits Holocene and Pleistocene

 Qo 44 Outwash Pleistocene

 Qob 304 Olivine basalt Pleistocene

 Qoba 305 Older basaltic andesite Pleistocene

 Qoe 45 Outwash of Evans Creek age Pleistocene

 Qsg 231 Rocks of Sandy Glacier volcano Pleistocene

 Qt 33 Talus Holocene and Pleistocene

QTa 242 Andesite Pleistocene or Pliocene

 QTab 243 Andesite of Badger Butte Pleistocene or Pliocene
Table 3. Numeric code values and map-unit symbols and names for stratigraphic units—Cont.

QTat 227 Andesite of Tom Dick and Ha rry Mountain Pleistocene or Pliocene

QTat? 228 Andesite of Tom Dick and Harry Mountain Pleistocene or Pliocene

 QTb 225 Basalt Pleistocene or Pliocene(? 

 QTba 421 Basaltic andesite Pleistocene or Pliocene(?)

QTbg 256 Basaltic andesite of Grasshopper Point Pleistocene or Pliocene

QTbme 234 Basaltic andesite of Mirror Lake and Eureka Peak Pleistocene or Pliocene

QTs 601 Sedimentary rocks and depos its Pleistocene and Pliocene(?)

 QTtla2 321 Volcanic rocks in Trillium Lake area, andesite Pleistocene or Pliocene 

 QTtlb 322 Volcanic rocks in Trillium Lake area, basalt Pleistocene or Pliocene

 Qv 61 Cinder cone or small volcano Quaternary

Qyba 301 Younger basaltic andesite Pleistocene

 Ta 427 Andesite Pliocene

 Taef 482 Andesite of East Fork Hood River Miocene

Taft 435 Andesite of Fi fteenmile Creek Pliocene

 Tafv 483 Andesite of Fivemile Butte Miocene

 Taj 438 Andesite of Jordan Butte Pliocene and Miocene

 Talb 437 Andesite of Little Badger Creek Pliocene

 Taop 561 Andesite of Lolo Pass Pliocene(?) and Miocene

 Taop? 562 Andesite of Lolo Pass Pliocene(?) and Miocene

 Tar 428 Andesite of Rocky Point Pliocene

 Tas 593 Andesite of Salmon Butte Miocene

 Tatc 547 Andesite of Tumble Creek Pliocene

 Tazm 581 Andesite of Zigzag Mountain Miocene

 Tb 548 Basalt Pliocene and (or) Miocene

 Tba 426 Basaltic andesite Pliocene

 Tbah 436 Basaltic andesite of Happy Ridge Pliocene

 Tbam 595 Basaltic andesite of Mack Hall Creek Miocene

 Tbao 423 Basaltic andesite of the Oak Grove Fork Pliocene

Tbas 439 Basaltic andesite of Sunset Spring Miocene

Tbbu 235 Basalt of Bull Run Watershed and other ridge-capping basalt Pliocene and Miocene(?) 

 Tbg 422 Basalt near Ghost Creek Pliocene or Miocene

 Tbj 549 Basalt of Juniper Flat Pliocene

Tcgn2 1003 CRBG, Grande Ronde Basalt, normal-polarity unit 2 Miocene

Tcgr2 1004 CRBG, Grande Ronde Basalt, reversed-polarity unit 2 Miocene

Tcwf 1002 CRBG, Wanapum Basalt, Fren chman Springs Member Miocene

Tcwpr 1001 CRBG, Wanapum Basalt, Pr iest Rapids Member Miocene

 Td 583 Dalles Formation Miocene

 Tdb 425 Dacite of Beaver Butte Pliocene 

 Tdgb 491 Dacite of Graveyard Butte Pliocene(?) or Miocene

 Tdl 429 Dacite north of Long Ridge Pliocene

 Tdm 481 Dacite of Mill Creek Buttes Miocene

 Tdp 594 Dacite of Plaza Lake Miocene

 Tfa 592 Fine-grained andesite Miocene

 Tha 424 Hornblende-bearing andesite Pliocene

 Tia 533 Intrusive andesite Pliocene and Miocene

Tiba 532 Intrusive basalt or basaltic andesite Pliocene

 Tilh 571 Intrusive rocks of Laurel Hill Miocene

Tlma 541 Lookout Mountain volcanic sequence, andesite Pliocene

Tlma? 542 Lookout Mountain volcanic sequence, andesite Pliocene

Tlmb 543 Lookout Mountain volcanic sequence, basalt Pliocene
Table 3. Numeric code values and map-unit symbols and names for stratigraphic units—Cont.

Tlmd 544 Lookout Mountain volcanic sequence, dacite Pliocene

Tlmd? 545 Lookout Mountain volcanic sequence, dacite Pliocene

Tma 591 Andesite of middle a nd late Miocene age Miocene

 Toa 431 Older andesite Miocene

 Toma 1112 Volcanic rocks of the Mutton Mountains, andesite Miocene and Oligocene

 Tomr 1113 Volcanic rocks of the Mutton Mountains, rhyolite Miocene and Oligocene

Tomt 1111 Volcanic rocks of the Mutton Mountains, tuff and tuffaceous sedimentary rocks Miocene and Oligocene 

 Tos 604 Older sedimentary rocks Miocene

 Tr 449 Rhyolite Pliocene or Miocene

Trbg 546 Rocks of Barlow Ridge and G unsight Butte Pliocene and Miocene

 Trgd 442 Rhyodacite of Gordon Butte, domes and flows Pliocene

Trgx 441 Rhyodacite of Gordon Bu tte, tuff breccia Pliocene

 Trh 582 Rhododendron Formation Miocene

 Ts 602 Sedimentary rocks Miocene

Ttla1 323 Volcanic rocks in Trillium Lake area, andesite Pliocene and (or) Miocene

 Ttv 451 Tygh Valley Formation Pliocene and Miocene(?)

Ttvp 452 Tygh Valley Formation, pyroclastic and sedimentary rocks Pliocene and Miocene(?) 

 Tv 531 Cinder cone or small volcano Tertiary

 Tvmf 563 Volcaniclastic rocks of Middle Fork of Hood River Miocene

Tvmf? 564 Volcaniclastic rocks of Middle Fork of Hood River Miocene

 Tvs 484 Volcaniclastic rocks Miocene

 Tys 603 Younger sedimentary rocks Pliocene and Miocene(?)

 u 2001 Unmapped

location or topologic rules for map ornamentation (table 

5). Additional structural features are fold axes, monocline 

hinges, and lineaments. Lineaments were mapped from air 

photos but lack notable expression in the field.

Radiometric K-Ar Ages (MH_KARages)

Complete age data for previously dated samples 

in the map area are compiled in table 1 of the included 

explanatory pamphlet. Noteworthy here is our decision 

to reassess some sample-location data that may have 

been misreported earlier. Consequently, map users should 

expect some slight visual shifts if the spreadsheet of ages 

is georegistered and superimposed on an image of the 

original map publication. Sample locations provided in 

the spreadsheet, and shown as revised in table 1 of the 

pamphlet, mark our best knowledge for sample positions as 

of 2014.
Table 4. Numeric code values for map-unit contacts.

Line 

Code Line Feature Line Symbol Explanation

10 Contact, precisely or Solid Contact exposed or can be estimated closely on basis of 

approximately located outcrops in adjacent units. In some places contact 

corresponds to abrupt break in slope and was placed on 

basis of air-photo mapping. Position has been determined 

by field work to within 100 m on the ground (1 mm on

map at 1:100,000 scale)

11 Contact, inferred or imprecise Short-dashed Geologic relations or ground surface morphology suggest 

contact present but not exposed and too uncertain to 

determine position more precisely than 100-200 m with 

confidence (as much as 2 mm at 1:100,000 scale)

12 Contact, internal Dotted Separates sequentially younger deposits in Polallie 

eruptive episode

13 Limit of propyllitic alteration Dot-dash Encloses an area of propyllitic clay alteration (shown 

patterned) in west-central part of map area between Still 

Creek and Salmon River, as mapped by Wise (1969)

15 Contact, figurative Hachured Boundary of areas unmapped or poorly mapped

16 Neatline Solid Edge of geologic unit owing to position of map neatline

17 Open-water boundary Solid Blue stroke

19 Scratch contact None (no stroke) Marks uncertain limit of tuff breccia (area shown 

patterned) within unit Trby at south end of Barlow Ridge 

where traverses were limited

41 Moraine crest Chained circles Crestline of ridges that formed as lateral moraines. 

Location approximate; drawn from air photos and 

topographic maps
Table 5 Table 5. Numeric code values and descriptions for structural features.

Line 

code Feature Line style Explanation

21 Normal fault, Solid, with ball and Fault exposed or displaced stratigraphic units sufficiently close 

approximately or bar on downthrown that position has been determined by field work to within 100 

well located side m on the ground (1.0 mm at 1:100,000 scale)

22 Normal fault, Short dashed

inferred 

24 Normal fault, Dotted Trace of fault concealed by younger stratigraphic unit; 

concealed positional accuracy uncertain but within 2 mm at 1:100,000 

(200 m on the ground) and commonly within 1.0 mm (100 m 

on the ground)

25 Reverse or thrust Solid, sawteeth on Right-hand rule for sawteeth ornamentation

fault upper plate

26 Reverse or thrust Dotted, sawteeth on Right-hand rule for sawteeth ornamentation

fault, concealed upper plate

28 Fault, type not Solid From Swanson and others (1981); may be oblique, reverse, or 

reported normal fault

31 Anticline Solid, with opposing Showing crestline and locally showing plunge; plunge 

arrowheads arrowhead at end-node of polyline

32 Syncline Solid, with converging Showing troughline

arrowheads

33 Monocline hinge, Solid Lower limb. Right-hand rule for ornamentation, with arrow 

abrupt decrease in symbols converging on hinge line

direction of arrow

34 Monocline hinge, Solid Upper limb. Right-hand rule for ornamentation, with 

abrupt increase in arrowheads diverging from hinge line

direction of arrow

35 Lineament Dash-dot Mapped from air photos. Origin most likely by small-offset 

faults or now-infilled ground cracks