Scientific Investigations Map 3260

Sheet 2 of 2

Pamphlet accompanies map

1000 1000 0 2000 3000 4000 5000 6000 7000 FEET

1 .5 0 1 KILOMETER

SCALE 1:24 000

CONTOUR INTERVAL 10 METERS

NATIONAL GEODETIC VERTICAL DATUM OF 1929

1 0 1/2 1 MILE

APPROXIMATE MEAN

DECLINATION, 2014

Base from U.S. Geological Survey 1:100,000-scale digital data, 1982

Universal Transverse Mercator, zone 10

North American Datum of 1983 (NAD 83)

Geologic mapping by Emily M. Taylor (2011–2013) 

Digital database prepared by Emily M. Taylor and

D. Paco Van Sistine

Edit and digital layout by Lisa Ramirez Rukstales

Cut bank (latest Holocene)

Fluvial and minor eolian deposits (latest Holocene)

Fluvial deposits (latest Holocene)

Fluvial deposits (late Holocene)

Fluvial deposits (late Holocene)

Fluvial and alluvial deposits (middle to early Holocene)

Fluvial and alluvial deposits (latest late Pleistocene)

Fluvial and alluvial deposits (latest late Pleistocene)

Eolian deposits (latest late Pleistocene)

Fluvial and alluvial deposits (latest late Pleistocene)

Fluvial and alluvial deposits (latest late Pleistocene)

Fluvial and alluvial deposits (early late Pleistocene)

Alluvial deposits (late middle Pleistocene)

Fluvial deposits (middle to early Pleistocene)

Paso Robles Formation (middle Pleistocene to Pliocene)

Shallow nearshore marine regressive sediments (Pliocene)

Pancho Rico Formation (Pliocene to Miocene)

Tertiary marine sediments (Miocene to Paleocene)

Undifferentiated basement rocks (Mesozoic to Paleozoic)

LIST OF MAP UNITS

Qcb

Qfr2

Qfr1

Qfy2

Qfy1

Qfay

Qfai4

Qfai3

Qfai2y

Qfai2o

Qfai1

Qao

QTpr

Tsa

Tpr

Tms

ub

Qfo8–1

Qei

Qfo8

Qfo7

Qfo5

Qfo4

Qfo3

Qfo2

Qfo1

Qfo6

QUATERNARY DEPOSITS BEDROCK

Holocene

Pleistocene

late

Pleistocene

middle 

Pleistocene

early 

Pleistocene

Pliocene

Paleocene

QUATERNARY

TERTIARY

MESOZOIC–

PALEOZOIC

Qfr2

Fluvial

deposits

 Fluvial and

Alluvial-fan 

deposits

Marine

sediments

[Angled boxes represent estimated range of age uncertainty; Holocene and Pleistocene subdivisions and boundary ages

are from Gibbard and others, 2010, p. 99]

CORRELATION OF MAP UNITS

Basement

Eolian

deposits

Qfr1

Qfy2

Qei

ub

Qfai3

Qao

Qfy1

Qfo8–

Qfo1

QTpr

Oligocene

Miocene

Eocene

Terrestrial

sediments

Qfai2y

Qfay

Qfai4

Qcb

Tpr

Tsa

Tms

Qfai2o

Qfai1

2.588 Ma

781 ka

126 ka

11,700 ± 99 ka

Qfo8

Qfo7

Qfo5

Qfo4

Qfo3

Qfo2

Qfo1

Qfo6

EXPLANATION OF MAP SYMBOLS

Contact

Faults—Solid where location is accurate; dashed where location is 

approximate or inferred; dotted where location is concealed

Thrust fault—Sawteeth on upper plate

Major rivers and drainages

Optically stimulated luminescence sample location and age— 

Sample number and ages are labeled on sheet 1 only outside 

of Arroyo Seco; sample numbers and ages within Arroyo 

Seco are labeled on sheet 2

Location of photographic viewpoint—Number indicates figure 

number on plate

AS10-9-8

1,590 ± 190 yrs

9

SOIL TYPES

[Soil types were identified using the soil map of Monterey County (Cook, 1978), 

in digital format (U.S. Department of Agriculture [USDA], 2009)]

Arroyo Seco gravelly sandy loam, Elder sandy loam

Chamise loam

Chualar loam

Fluvents stony

Lockwood loam

Metz loamy sand, Moncho silty loam, Pico sandy loam

Placentia sandy loam

Psamments, Fluvents

Rincon clay loam

Tujunga sand

Qfai2y

Qfai2y

Qfai2y

Qfai2y

Qfai2y

ub

Qfai3

Qcb

Qfai3

Qfo7

Qfai2y

Qfai3

Qfai3

Qfai3

Qfai3

Qfai2y

Qfai2y

Qfai3

Qfy1

Qfai3

Qfai3

Qfai2o

Qfai3

Qfai3

ub

ub

Qfo7

Qfai2o

Qfai2o

Qfai3

Qfr1

Qfr1

Qfai3 Qfai3

Qfr2

Qfr2

Qfai3 Qfai3 Qfai3

Qfai2y

Qfai2y

Qfai3

Qfai2y

Qfai2y

Qfai3

Qfai3

Qfai3

Qfr1

Qfr1

Qfr1

Qfai3

Qfai3

Qfai3

Qfr1

Qfr1

Qfai3

Qfai3

Qfo7

Qfai2y

Qfai1 Qfai2o

Qfai1

Qfai1

Qfai1

Qfo8

Qfo8

Qfy1

Qfai2y

Qfai2y

Qfai2y

Qfo8

Qfo7

Tms

Tms

Tms

Tms

Tms

Tms

Tms

Tms

Tms

Tms

Qfy1

Qfy1

Qfai2o

Qfai1

Qfy1

Qfo7

Qfai1

Qfai1

Qfai2o

Qfai1

Qfai1

Qfai1

Qfai2o

Qfai2o

Qfo8 Qfo8

Qfai2o

Qfai2o

Qfai2o Qfai1

Qfai1

Qfai2o

Qfai1

Qfai2y

Qfai2y

Qfai2o

Qfay

Qfr1

Qfr1

Qfai2y

Qfai2o

Qfr2

Qfai3

Qfo7

Qfo5

Qfai2o

Qfo3

Qfai1

Qfai1

Qfai1

Qfai1

Qfai1

Qfai1

Qfai2o Qfai1

Qfy1

Qfay

Qfy1

Qfy1

Qfy1

Qfy1

Qfay

Qfay Qfai3

Qfr1 Qfr2

Qfy1

Qfai4

Qfai4

Qfai3

Qfo8

Qfo8

Qfo8

Qfo7

Qfo7 Qfo7

Qfai2y

Tpr

QTpr

Tsa

Qfai1

Qfai1

Qfai1

Qfai2y

Qfai4

Qfai4

Qfai4

Qfai3

Qfai3

Qfai3

Qfr1

Qfai3

Qfai4

Qfy1

Qfai2y Qfai2o

Qfy1

Qfai1

Qfai2o

Qfai2y

Qfai3

Qfai4

Qfai2o

Qfay Tsa

Tsa

QTpr

Qfai1

Qfai3

Qfay

Qfay Qfai4

Qfai3

Qfai1

Qfai1

Qfai1

QTpr

Qfai1

Qfai2o

Qfai1

Qfay

Qfr1

Qfy1 Qfy1

Qfy2 Qfy2

Qfay

Qcb

Qfy1

Qfy1

Tpr

QTpr

Tsa

Qfai2o

Qfo3 Qfo4

Qfo7

Qfo7

Qfai2o

Qfai2y

Qfo7

Qfo5

Qfo1

Qfo2 Qfo3 Qfo2

Qfo7

Tms

Qfo7

Qfo8

Qfo3

Qfo7

Qfo6

Qfo1

Qfo1

Qfo7

Qfo7

Qfo7

Qfo7

Qfo8

Qfo5

Qfo4

Qfai2y Qfai3

Qfai3

Qfr2

Qfai2o

Qfai2y

Qfy1

Qfy1 Qfai3

Qfy1

Qfy1

Qfo3

Qfai1 Qfo8 Qfo6

Qfo7

Qfai1

Qfai1

Qfai2o Qfai1

Qfai2y

Qfo8

Qfo7

Qfo8

Qfo8 Qfai1

Qfo8

Qfai1

Qfy1

Qfai3

Qfay

Qfr1

Qfr1

Qfai4 Qfy1

Qfai3

Qfr1

Qfai2o

Qfai1

Qfo7

Qfo6

Qfo7

Qfo6

Qfo5

Qfo4

Qfo4

Qfai2o

Tsa

Tsa

Tsa

Qfr2

Qfr2

Qfr1

Qfr2

Qcb

Qcb

Tsa

Qfr1

Tpr

Qfai3

Qfai3

121°30’

16’

36°14’

28’

24’

26’

121°30’

28’

28’

16’

26’

28’

24’

22’

20’

121°18’

36°18’

36°18’

121°18’

22’

20’

36°14’

Figure 15. Photograph looking downstream at a well-preserved sequence of late Pleistocene and inset Holocene strath terraces (see map for location of photographic viewpoint). Where Arroyo Seco 

has eroded Tertiary marine sediments, primarily Monterey shale, a broad valley has formed. Each terrace records a floodplain eroded into the bedrock and is capped by rounded gravel derived from 

the more resistant basement rocks (ub) upstream. Photograph by Tony Garcia, California Polytechnic University, San Luis Obispo, 2012.

Qfy1

Tms Qfy1

Qfai3 Qfai3 Qfai3 barn

Qfai4

ub

Qfai4

Qfai4

QTpr

Qfai1

Qfr1

Monroe

Canyon

Thompson Thompson

Canyon

Pine

Canyon

Reliz Canyon Reliz Canyon

Monroe

Canyon

Thompson

Canyon

Pine

Canyon

Reliz Canyon

01234

0123 4

5 MILES

5 KILOMETERS

Paloma

Piney

Creek

Creek

Arroyo

Seco

Chalone Creek

Salinas River

121°30' 121°20' 121°10'

36°10'

36°20'

B

Greenfield

101

Area of inset map

King

City

Figure 14. Location of inset map showing Arroyo Seco and the Quaternary terraces.

EXPLANATION

Fault

Highway

River or drainage

Figure 13. This fault exposure is preserved in the road cut on the 

north side of the bridge that crosses the mouth of Arroyo Seco (see 

map for location of photographic viewpoint). The Reliz fault, 

exposed in a road cut in Arroyo Seco, has a dominant reverse 

dip-slip movement. Sheared rock and gouge separate the Pancho 

Rico Formation from the Monterey Formation. In the photograph, 

“A” indicates strike-slip movement away from the viewer and “T” 

indicates strike-slip movement toward the viewer. At this location, 

the Pleistocene fluvial-terrace gravels appear preserved above the 

Monterey Shale and downslope above the Pancho Rico Formation.

Unfaulted late Pleistocene 

fluvial-terrace deposits

Monterey Formation

(Tms)

Pancho Rico Formation

(Tpr)

A T

A T

Figure 12. Small terrace treads are preserved in the narrow Arroyo Seco canyon (see 

map for location of photographic viewpoint). These strath terraces record where the 

Arroyo Seco floodplain once eroded the undifferentiated basement rocks (ub). 

White dashes locate the terrace surface and yellow dashes locate the top of bedrock. 

Gravels are about 1 meter thick.

Terrace gravel Terrace gravel errace gravel

Undifferentiated

basement rocks

Figure 11. This is a view looking upstream of Arroyo Seco where it is confined in a 

narrow canyon (see map for photographic viewpoint). Resistant basement bedrock 

(ub) prevents a broad alluvial floodplain from forming. Downstream, less 

resistant Tertiary marine sediments are eroded by the Arroyo Seco and the sequence 

of strath terraces is preserved.

Arroyo Seco stream gradient

50

150

250

350

450

550

650

750

0 5,000 10,000 15,000 20,000 25,000 30,000 35,000 40,000 45,000

Elevation, in meters

Distance down Arroyo Seco drainage, in meters

Low broad

continuous

surfaces

High small

terrace

remnants

EXPLANATION

Map Units

Qfr1

Qfy1

Qfay

Qfai4

Qfai3

Qfai2y

Qfai2o

Qfai1

Qfo8

Qfo7

Qfo6

Qfo5

Qfo4

Qfo3

Qfo2

Qfo1

Figure 10. Stream gradient profile of terrace surfaces along Arroyo Seco. Different colored symbols represent different terrace surfaces. Terraces are 

approximately parallel and range in elevation from 100 to 800 m. The highest erosional features (Qfo1–Qfo1) are associated with the paleoerosional 

surface in the northwest corner of the mapped Tertiary marine sediments. Intermediate elevation terrace remnants occur on both the north and south 

sides of Arroyo Seco (Qfo7–Qfo8). Map unit Qfai1 is a strath surface often eroded on the Paso Robles (QTpr) and the Pancho Rico Formations (Tpr). 

Lower terraces are typically broad and continuous along the modern Arroyo Seco (Qfai2o–Qfr1).

Sample number 

(geologic map unit, 

soil) Latitudea Longitudea

% Water 

contentb K (%)c U (ppm)c Th (ppm)c

Cosmic dosed

additions 

(Gy/ka)

Total dose rate 

(Gy/ka)

Equivalent dose 

(Gy) ne Age (yrs)f

AS10-9-7

(Qfy1, Fluvent) 36.266 -121.351 0 (29) 2.83 ± 0.04 1.85 ± 0.13 7.49 ± 0.27 0.18 ± 0.01 3.46 ± 0.08g 5.41 ± 0.65g 23 (30) 1,030 ± 150g

AS10-9-8

(Qfy1, Fluvent) 36.260 -121.366 2 (27) 2.42 ± 0.03 2.30 ± 0.12 10.5 ± 0.27 0.18 ± 0.01 3.40 ± 0.07g 3.57 ± 0.52g 14 (20) 1,590 ± 190g

AS12-6-1

(Qfay, Arroyo Seco) 36.324 -121.230 1 (21) 3.61 ± 0.05 1.43 ± 0.07 6.74 ± 0.27 0.17 ± 0.01 4.19 ± 0.10f 40.1 ± 2.69f 16 (28) 9,570 ± 680g

AS12-6-2

(Qfai4, Rincon) 36.318 -121.303 0 (21) 3.00 ± 0.04 1.37 ± 0.08 6.62 ± 0.22 0.18 ± 0.01 3.63 ± 0.08f 31.9 ± 1.08f 16 (24) (8,770 ± 350g

)

h

AS12-6-3

(Qfai3, Chualar) 36.275 -121.328 1 (26) 2.24 ± 0.03 1.92 ± 0.11 10.6 ± 0.35 0.17 ± 0.01 4.45 ± 0.11 157 ± 15.7 28 (30) 35,350 ± 3,680

AS10-9-9

(Qai2y, Lockwood) 36.263 -121.408 0 (37) 1.57 ± 0.02 1.93 ± 0.09 8.70 ± 0.20 0.19 ± 0.01 3.61 ± 0.08 182 ± 9.10

166 ± 5.66

30 (30)

29 (30)

50,640 ± 2,980

45,960 ± 1,840

AS10-9-6

(Qfai2o, Lockwood) 36.268 -121.358 0 (32) 2.51 ± 0.03 1.90 ± 0.15 9.57 ± 0.29 0.07 ± 0.01 4.80 ± 0.10g >210g 13 (20) >65,000g

AS10-9-5

(Qfai1, Placentia) 36.284 -121.320 0 (31) 2.23 ± 0.03 1.98 ± 0.10 8.52 ± 0.24 0.13 ± 0.01 4.16 ± 0.09 >500 18 (20) >120,000

e

Number of replicated equivalent dose (De) estimates used to calculate the mean. Figures in parentheses indicate total number of measurements made including failed runs with usable data

f

Dose rate and age for fine-grained 250–180 μm potassium feldspar grains. Linear + exponential fit used on age, errors to one sigma. Fade tests indicate correction of 5–10%. Fade tests indicate a g value of 1%/decade. For the samples already in

saturation (AS10-9-5 and AS10-9-6) this value has not been added.

g

Dose rate and age for finer-grained 250–180 μm quartz sand. Linear + exponential fit used on equivalent dose, errors to one sigma, single aliquot regeneration (SAR). 

a

Projected coordinates are in UTM Zone 10, NAD 83

b

Field moisture, with figures in parentheses indicating the complete sample saturation %. Ages calculated using approximately 50% of saturation values. c

Analyses obtained using laboratory gamma spectrometry on a bulk sample (high-resolution Ge detector).

d

Cosmic doses and attenuation with depth were calculated using the methods of Prescott and Hutton (1994).

Table 3. Single aliquot regeneration feldspar infrared stimulated luminescence (IRSL) and quartz optically stimulated luminescence (OSL) ages from Arroyo Seco area, California. Sample 

locations are shown on 1:50,000 Arroyo Seco geologic map, sheet 1; all sample locations except AS12-6-1 and AS12-6-2 are shown on sheet 2. Dates were obtained by using standard methods 

described in Mahan and Brown (2007). [%, percent; K, potassium; U, uranium; ppm, parts per million; Th, thorium; Gy, Gray or absorbed radiation energy per unit mass; ka, kilo-annum, 

103 years; yrs, years] 

h

Questionable result.

RELIZ FAULT

RELIZ

FAULT

WILLOW

ARROYO

CREEK SECO

FAULT

FAULT

PALOMA

PINEY

CREEK

CREEK

U.S. Department of the Interior

U.S. Geological Survey

This report is available at:

http://pubs.usgs.gov/sim/3260

Suggested citation:

Taylor, E.M., and Sweetkind, D.S., 2014, Quaternary geologic map of the north-central part of the Salinas 

River Valley and Arroyo Seco, Monterey County, California: U.S. Geological Survey Scientific Investigations 

Map 3260, 13 p., 2 sheets, scales 1:24,000 and 1:50,000, http://dx.doi.org/10.3133/sim3260.

Publishing support provided by:

Denver Publishing Service Center

Manuscript approved for publication May 14, 2014

To learn about the USGS and its information products visit

http://www.usgs.gov/

1-888-ASK-USGS

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

endorsement by the U.S. Government

This database, identified as SIM 3260, has been approved for release and publication by the 

U.S. Geological Survey (USGS). Although this database has been subjected to rigorous review 

and is substantially complete, the USGS reserves the right to revise the data pursuant to 

further analysis and review. Furthermore, it is released on condition that neither the USGS or 

the U.S. Government may be held liable for any damages resulting from its authorized or 

unauthorized use.

For more information concerning this publication, contact:

Center Director, USGS Geosciences and Environmental Change Science Center

Box 25046, Mail Stop 980

Denver, CO 80225

(303) 236-5344

Or visit the Geosciences and Environmental Change Science Center

Web site at: http://gec.cr.usgs.gov

ISSN 2329-132X (online)

2014 http://dx.doi.org/10.3133/sim3260

Emily M. Taylor and Donald S. Sweetkind

By

Inset map of Arroyo Seco and Quaternary Terraces

Quaternary Geologic Map of the North-Central Part of the Salinas River Valley and Arroyo Seco, Monterey County, California

AS10-9-5

>120,000 yrs

AS12-6-3

33,350 ± 3,680 yrs

AS10-9-6

>65,000 yrs

AS10-9-8

1,590 ± 190 yrs

AS10-9-9

50,640 ± 2,980 yrs

45,960 ± 1,840 yrs

AS10-9-7

1,030 ± 150 yrs

12 11

15

13