Terrace Formation in the Upper Headwater Region of The

TERRACE FORMATION IN THE UPPER HEADWATER REGION OF THE

MATTOLE RIVER WATERSHED ACROSS THE MENDOCINO TRIPLE

JUNCTION, NORTHWEST CALIFORNIA

Michelle L. Robinson

A Thesis Presented to

The Faculty of Humboldt State University

In Partial Fulfillment of the Requirements for the Degree

Master of Science in Environmental Systems: Geology

Committee Membership

Dr. Mark Hemphill-Haley, Committee Chair

Sam Flanagan II, M.Sc., Committee Member

Dr. Andre Lehre, Committee Member

Dr. Rick Zechman, Program Graduate Coordinator

May 2016

ABSTRACT

TERRACE FORMATION IN THE UPPER HEADWATER REGION OF THE MATTOLE RIVER WATERSHED ACROSS THE MENDOCINO TRIPLE JUNCTION, NORTHWEST CALIFORNIA

Michelle L. Robinson

The Mattole River, in northwestern California, is located in a tectonically active

and geologically complex area, the Mendocino triple junction (MTJ), where the North

American, Pacific and Gorda plates meet. The Mattole River does not follow the classic

river “concave-up” profile. Instead, the river headwaters have wide valleys of low

gradient terraces with deeply incised active channels. As a result of differential uplift

along the river, the longitudinal profile has two “convex-up” sections resulting in low gradients in the headwaters leading to higher gradients in the midcourse. Low gradients have accommodated terrace formation in the upper headwater region of the Mattole

River, that record times of disequilibrium as the river responds to changes that are, in

part, due to changes in climate and also the passage of the northwardly migrating MTJ

and associated growth of a slab window. Age estimates of sediments in Baker Creek,

determined using optically stimulated luminescence dating (OSL), suggest the timing of

valley widening and filling occurred after the LGM to 17 ka and from 11 to 8 ka. Surveys

of terrace surfaces were conducted along four headwater tributaries: Ancestor Creek,

Baker Creek, Lost River and Thompson Creek. Similar flights of terraces in three of the

four surveyed headwater tributaries, along with locations of knickpoints and convexities in the long profile, provide information about the fluvial system’s response to changes in climate and the ongoing northward migration of the MTJ.

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ACKNOWLEDGEMENTS

I would like to give a huge and very special thanks to the Humboldt State

University Geology department faculty and staff for igniting my love of geology and providing the greatest learning environments in the field, in the lab and in the classroom.

Endless thanks to my advisor Dr. Mark Hemphill-Haley for unlimited support and respect, and always making time to give geological and life advice. Thank you to Sam

Flanagan and his infinite Mattole wisdom, without whom this project would never have been possible, and the BLM for providing funding through F2957 and F3026 Upper

Mattole River projects. Thank you to Sanctuary Forest, especially Tasha McKee, for allowing me to assist in surveying and giving me access to the tributaries, and Katrina

Nystrom, for providing well data. Thanks to Keith Barnard for showing me the total station ropes and processing the topographic data. A big thank you to Dr. Andre Lehre for encouraging and supporting me even before I became a geology major and for being a member of my graduate committee. Thanks to Dr. Bud Burke for being the climate master and sacrificing so much time and effort to share his wisdom. Major thanks to

Shannon Mahan for making the time, and allowing me to process my OSL samples in her lab at the USGS Luminescence Dating Lab in Denver, Co. Thanks to Harrison Gray and

Candice Passehl at the USGS lab for showing me how to process my samples and work in the dark. Thank you to Melissa Foster for introducing me to Shannon and being supportive of my research. Thank you to my generous field assistants: Colin Wingfield, for suffering through terrible poison oak while helping survey all four tributaries and for iv

digging a hole as deep as he is tall; Christa Anhold for helping sample for OSL and being

the positive support I needed in a time of uncertainty, Ed Welter for not shying away

from scary gates while surveying and Bella the dog for making field work look like a nap

in the forest. Thanks to Jay Stallman for valuable insight into how rivers respond to

climate. I greatly appreciate my geological sisters: Jessie Vermeer, for being by my side through both our undergraduate and graduate research endeavors and Sylvia Nicovich for

never ending support and showing me what it takes to be a great graduate student, TA

and respectful human being. Thanks to Steve “Beaver” Tillinghast for teaching me to be

a field geologist and how to drive dirt roads like a champion. Thanks to Eileen Hemphill-

Haley for such a great first experience with research, as a senior undergraduate, that

motivated me to do more. One million thanks to Laurie Marx, the most helpful individual

on the planet, for always assisting me with paperwork, providing me with sugar and

teaching me valuable life lessons. Last, but not least, thanks to my GIS lab buddies: Evan

Hartshorn and Aaron Katz, for their constant presence and positive attitudes.

TABLE OF CONTENTS

ABSTRACT ...... ii

ACKNOWLEDGEMENTS ...... iv

LIST OF TABLES ...... viii

LIST OF FIGURES ...... ix

INTRODUCTION ...... 1

GEOLOGIC SETTING ...... 7

METHODS ...... 14

Geomorphic Mapping and Surveying ...... 14

Auger Hole Data ...... 18

Optically Stimulated Luminescence Age Estimates ...... 19

DEM Analysis ...... 22

RESULTS ...... 25

Terraces and Relative Ages ...... 25

Bedrock Topography and Terrace Stratigraphy ...... 27

Absolute Ages of Terraces ...... 28

Longitudinal Profiles ...... 31

DISCUSSION ...... 36

Fluvial Terrace Sequences ...... 36

Paleoclimate ...... 38

Late Pleistocene Holocene Terrace Formation ...... 40

Terrace Formation Model ...... 43 vi

Relation of Mattole River to MTJ Region ...... 45

CONCLUSIONS...... 50

REFERENCES ...... 52

APPENDIX ...... 58

vii

LIST OF TABLES

Table 1. Terrace sequences in headwater tributaries from cross sectional surveys based on elevation above the active channel thalweg...... 27

Table 2. Terrace thickness and incision rates using OSL ages of sediments from Baker Creek ...... 38

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LIST OF FIGURES

Figure 1. Regional tectonic map of northern California showing major faults and locations of marine terrace sites used to infer uplift rates from Merritts (1987). ources of data: Bryant (2005); Davenport (2002); Esri and NOAA. CSZ, Cascadia subduction zone; MFZ, Mendocino fracture zone; SAF, San Andreas fault; LSF, Little Salmon fault; MRFZ, Mad River fault zone...... 2

Figure 2. Regional location map of northern California showing published rates of uplift along the coast, near the Mendocino triple junction (shown by diagonal lines in shaded ellipse). Prior locations of the Mendocino triple junction are indicated for 1 and 2 Ma. Figure modified from Merritts and Vincent (1989, figures 1 and 2). . 3

Figure 3. Modeled patterns of uplift associated with crustal deformation due to the migration of the MTJ A) Latest Pleistocene (<72 ka) uplift rates plotted along a N30W transect from near Cape Mendocino (0 km) to Fort Bragg (~120 km). Locations of the southern edge of subducted Gorda slab are plotted at top of diagram. Uplift rates determined from dated marine terraces (A1-H). Figure modified from Merritts and Vincent (1989, figure 4). B) Locations of two small stream drainage divides, controlled by the position of the peaks in the pattern of uplift (black double-humped profile). Figure modified from Lock et al. (2006, figure 9). C) Cartoon shows deformation of the North American plate in response to the northward migration of the Mendocino triple junction. Length of arrows indicate relative amount of uplift. Circular arrows show upwelling magma...... 5

Figure 4. Topographic map of Mattole River watershed showing headwater tributaries of interest and locations of marine terrace sites used to infer uplift from Merritts (1987). Sources of data: Davenport (2002); USGS NED (2013); Esri and NOAA (2015). Marine terrace sites: B, Kaluna Cliff; C, Randall Creek; D, Smith Gulch; E, McNutt Gulch...... 8

Figure 5. Figure Topographic map of headwater region of the Mattole River watershed showing tributaries of interest and locations of cross-sectional surveys. Sources of data: Davenport (2002); USGS NED (2013)...... 9

Figure 6. Geologic map of the Mattole River watershed showing geologic units and faults. Sources of data: Bryant (2005); Davenport (2002); USGS NED (2013); Esri and NOAA (2015)...... 11

Figure 7. Baker Creek topography shown by a Triangular Irregular Network generated in ArcGIS 10.1 from total station survey data. Black circles indicate locations of hand dug monitoring wells (e.g. WELL 19, NIWI), auger holes (e.g. A28) and OSL sample sites (e.g. BT4). Note elevations in this model are shown in feet. ... 16

Figure 8. Cross section surveys of headwater tributaries of interest. Surveys were measured in feet and are represented here in feet above the active channel thalweg. Note differing scales and vertical exaggerations. Sources of data: USGS NED (2013)...... 17

Figure 9. Stratigraphy of Optically Stimulated Luminescence (OSL) sample locations showing sample name, elevation and depth. Scales on left and bottom shows relative elevation above active channel in feet above the thalweg and flow direction. Note scales are in feet due to all topographic surveys being measured in feet...... 21

Figure 10. Method of comparing valley center and longitudinal profiles by plotting the elevation of the thalweg where it crosses the valley center line with respect to the valley center line distance in order to remove the effects of sinuosity. A) Example of section of thalweg or active channel, B) Valley center line, C) Points used in plot of less sinuous thalweg, D) Points used in plot of valley center with active channel buffer. Sources of data: Davenport (2002); USGS NED (2013)...... 24

Figure 11. Terrace map of Baker Creek. Terraces mapped on high resolution topographic contours generated from survey data measured in feet and are shown in feet ..... 26

Figure 12. Bedrock topography in Baker Creek. Topography (solid black lines) and resulting bedrock elevations (dashed grey lines) were surveyed in feet and are shown in feet. Also shown are channel cross sections (solid black line) with bedrock topography (dashed black lines) showing bedrock strath benches. From bedrock elevations, terrace thicknesses could be determined and used to calculate incision rates. Note poor resolution of background DEM (in meters)...... 29

Figure 13. Quartz OSL data and dates for Baker Creek, in the headwaters of the Mattole River, CA ...... 30

Figure 14. Longitudinal profiles of headwater tributaries of interest showing surveyed terraces. Note differing vertical exaggerations and scales, steplike features reflect resolution of DEM, not morphology of channel bed. Scales are shown in feet as a result of survey data measured in feet. Sources of data: USGS NED (2013)...... 32

Figure 15. Long profile of the Mattole River, the Mattole valley center line and the topographic profile of the western boundary of the Mattole River watershed. Deviations in the valley center profile from the Mattole River longitudinal profile show areas of preserved valley terraces or old valley bottoms. Note where convexities occur in the longitudinal profile are also areas of high relief between the Mattole River and the watershed profile. Sources of data: Davenport (2002); USGS NED (2013)...... 34

Figure 16. Longitudinal profile of headwater region of Mattole River including tributaries of interest. Note knickpoints downstream of Baker Creek and downstream of Ancestor Creek. These knickpoints will continue to adjust the gradients of the river towards equilibrium as they migrate upstream. VE, Vertical Exaggeration. Sources of data: Davenport (2002); USGS NED (2013)...... 35

Figure 17. Correlation of channel widening/fill timing of Terrace 2/3 and Terrace 4/5 in the headwaters tributaries of the Mattole River with organic carbon records at Eel River Basin Ocean Drilling Program site 1019 (Lyle, 2000), showing the Younger Dryas interval based upon the radiocarbon age model of Mix et al. (1999) and positions of the three laminated (high abundance of upwelling diatom flora) intervals during deglaciation. Valley widening/filling occurs during warm and wet interglacial intervals producing high sediment loads, incision at 17 ka and 8ka preserves terraces above the active channel. A, alder; RW, redwood. Figure modified from Lyle et al. (2000)...... 42

Figure 18. Proposed models for terrace formation and timing in the Mattole River headwaters region. Different colors correspond to different fill deposits. Model A shows proposed model of terrace formation including bedrock strath contraints, Model B shows formation of terraces with bedrock topography being generated during incision. HW; headwaters...... 44

Figure 19. Generalized aggradational and degradational response of a stream profile as it crosses a dome of rock uplift. This is the general scenario taking place in the Mattole River watershed as it adjusts to deformation associated with the MTJ slab window. Area 1 corresponds to the headwaters of the Mattole, upstream of the southernmost convexity, area 4 corresponds to the region just downstream of the northernmost convexity in the Mattole long profile. Figure modified from Holbrook and Schumm (1998, figure 3)...... 46

Figure 20. Map of Mattole River watershed showing areas where convexities occur on the long profile (solid ellipse) and where inferred preserved terraces from deviations of the valley center profile and the long profile occur (dashed ellipse). Note how these features spatially align with areas of highest relief in the watershed. Also shown the peaks in uplift from two models of deformation associated with the crustal deformation from the slab window or MCC. Note how these models also spatially align with not only each other but the major features of the Mattole River. Locations of peaks in uplift from Merritts and Vincent (1989, figure 4) and Lock et al (2006, figure 9). Sources of data, USGS NED (2013); Esri and NOAA (2015)...... 49

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INTRODUCTION

The Mattole River is located in a tectonically active and geologically complex region, the Mendocino Triple Junction (MTJ), where the North American, Gorda and

Pacific plates meet (Figure 1). Areas within the influence of the MTJ, including the

Mattole River watershed (Figure 2), experience some of the highest rates of crustal deformation and surface uplift in North America (Lajoie 1982, Lock et al., 2006;

Merritts, 1996; Merritts and Bull, 1989; Merritts, Vincent and Wohl, 1994). Previous studies within the MTJ region focus on tectonic uplift and crustal deformation (Clarke and Carver, 1992; Dumitru, 1991; Furlong and Govers, 1999; Lajoie, 1982; Lock et al.,

2006; McCory, 2000; McPherson et al., 2010; Merritts, 1996; Merritts and Bull, 1989), fluvial responses to base level change and stream piracy (Koehler, 1999; Merritts and

Vincent, 1989; Merritts, Vincent and Wohl, 1994; Pazzaglia, Gardner and Merritts, 1998;

Personius, 1995; Wegmann and Pazzaglia, 1998) and plate boundary evolution (Atwater,

1970; Furlong and Schwartz, 2004; Prentice et al., 1999; Mclaughlin et al., 1994;

Mclaughlin et al., 2000).

Uplift rates have been estimated using dated Holocene and late Pleistocene marine terraces at the coast, along the length of the Mattole River. Merritts and Bull

(1989) indicate accelerated uplift rates occur during and after the passage of the MTJ, with rates just under 2 m/ka at the present day junction, 4 m/ka 25-40 km south of the

MTJ and rates of at least 1 m/ka at Point Delgada, 55 km south of the MTJ, near the headwaters of the Mattole River. A similar study by Merritts and Vincent (1989)

examined the gradients of 24 coastal watersheds and their morphological properties with

comparable results, showing a similar pattern in peak uplift, with the highest uplift rates

occurring around the MTJ and decreasing to the south. Other studies have produced uplift

models to explain observed structures and landforms further inland, also relating to the

passage of the MTJ and the resulting slab window (Furlong et al., 1989; Furlong and

Govers, 1999; Furlong and Schwartz, 2004; Lock et al., 2006) (Figure 3).

Drainage basins in northwestern California have been adjusting to crustal

deformation and surface uplift associated with the northward migration of the MTJ and

resulting growth of a slab window throughout the Quaternary (Lock et al., 2006; Merritts

and Vincent, 1989). Superimposed on the tectonic signal being recorded by rivers in this

region, are changes in discharge and sediment loads related to glacial-interglacial climate cycles (Barron et al., 2003; Hancock and Anderson, 2002; Stallman, 2003). Fluvial terraces and longitudinal profiles of rivers record the evolution of drainage basins.

Eustatic and tectonic base level changes, differing rates of uplift and climate related changes in sediment supply and stream power are the main factors controlling disequilibrium and channel incision in a fluvial system (Merritts, 2007; Merritts and

Vincent, 1989; Merritts et al., 1994; Pazzaglia and Brandon, 2001; Pazzaglia et al., 1998;

Personius, 1995; Wegmann and Pazzaglia, 2009).

Convexities in the Mattole river longitudinal profile evidence the river’s response to changes in equilibrium (Kirby and Whipple, 2012; Koehler, 1999; Stallman, 2003).

Contrary to typical streams, the Mattole River (Howard, 1998) headwater region has wide, relatively low gradient valleys in the main stem and its tributaries, where the active

channels are also deeply incised. Variation in uplift rates along the length of the Mattole

River, due to deformation associated with the MTJ, combined with changes in climate

and anthropogenic modification of the landscape, have led to atypical conditions in the

headwaters.

Efforts to restore healthy ecosystems in the Mattole watershed have been taking

place for decades in a variety of different projects. (MRRP, 2009; Sanctuary Forest Inc.,

2014). Flows in the upper reaches of the Mattole have been monitored for more than 60 years (Sanctuary Forest Inc., 2014) and some of the lowest flows have been recorded

during the last 10 dry seasons. Understanding how the Mattole River responds to changes

in tectonic and climactic signals and the timing and formation of geomorphic features in

the watershed could assist in understanding the landscape’s sensitivity to future changes.

This research focuses on the formation of terraces in four tributaries in the

headwater region of the Mattole River with the following objectives: 1) evaluate the

relative ages of terrace sequences; 2) investigate the origin of the terraces with possible

terrace forming mechanisms being climate and tectonics; 3) establish the timing of

terrace formation events consistent with relative ages and origins of terraces; and 4) relate

river morphology and terrace timing with the northward migration of the MTJ and its

passage through the river’s course.

GEOLOGIC SETTING

The Mattole River headwaters originate less than 5 km from the coast near Point

Delgada in Shelter Cove, California (Figure 4). At its origin, the river flows east a few

miles then turns to flow north-northwest for roughly 97 km before exiting north of the

King Range into the Pacific Ocean, about 48 km south of Eureka, at the present day MTJ.

The river’s elevation ranges from sea level to 490 m; the maximum elevation of the

bounding watershed reaches 1200 m. Field studies of terrace formation were located in

four of the tributaries to the main stem Mattole within 8 km from its origin (Figure 5).

The Mattole watershed receives an average of 114 cm precipitation annually near the mouth, and up to 290 cm in the headwaters (Coates et al., 2002). 90% of the precipitation occurs as rainfall during the winter months and coastal fog is common in the north and western parts of the watershed. High intensity rainfall in the winters and warm, dry summers characterize the Mediterranean climate of this area. Average annual temperatures often vary only 10 degrees Fahrenheit (Coates et al 2002; Davenport et al.,

2002; MRRP, 2009).

Vegetation in the watershed is a mix of grassland and mixed conifer and hardwood forests. Grasslands occur mostly in the north, close to the mouth. Forests of

Douglas fir, tan oak and redwood with madrone and alder, dominate in the south, with the headwaters being 95% forested. (Coates et al., 2002; Heusser et al., 2000; Sanctuary

Forest Inc., 2014; MRRP, 2009) Mattole forests are denser and younger than they have been in the past. Most of the trees measure less than 60 cm diameter at breast height due

to a combination of fire suppression and logging (Sanctuary Forest Inc., 2014; Coats et

al., 2002).

Current land use in the headwater region of the Mattole River is mostly industrial

forestlands and conservation lands with scattered residential parcels. The most intense

harvesting of timber took place throughout the entire watershed between 1945 -1961.

During this time vegetation was removed and thousands of logging roads constructed,

mobilizing sediment in the drainages, changing water chemistry and disrupting fluvial

processes (Coates et al., 2002; Davenport et al., 2002; Sanctuary Forest Inc., 2014;

MRRP, 2009)

The Mattole River flows through the Coastal terrane in the Coastal belt of the

Franciscan complex, east of the King Range terrane (Figure 6). The accretionary

assemblage of the Franciscan complex is divided into three broad belts, which become

younger to the west. The westernmost Coastal belt is comprised of Pliocene to Late

Cretaceous sandstones and argillites that are highly sheared, folded and broken

(Davenport et al., 2002; Mclaughlin et al., 2000). The Coastal belt is divided further into

several structural terranes. The Coastal terrane is in contact with the Yager terrane to the

east and the King Range terrane to the west. The Coastal terrane contains mélange, highly

folded argillite and shattered sandstone and some lenses of Late Cretaceous basaltic rocks

(Mclaughlin et al., 1994). While there are variable amounts of shearing and few differing rock types in this unit, the lithology of the Mattole can be considered relatively uniform for this study.

Figure 6. Geologic map of the Mattole River watershed showing geologic units and faults. Sources of data: Bryant (2005); Davenport (2002); USGS NED (2013); Esri and NOAA (2015).

The MTJ is the approximate juncture of the Cascadia subduction zone (CSZ), the

Mendocino fault (MF) and the San Andreas fault (SAF) (Figure 1). North of the MTJ, the

Gorda plate subducts beneath the North American plate along the CSZ. South of the

MTJ, the Pacific plate moves northwestward relative to North America along the San

Andreas fault system, a zone of dextral slip faults that includes the SAF, Maacama, and

Bartlett Springs faults. Initiation of the MTJ occurred roughly 30 Ma when transform

motion replaced subduction as the spreading ridge between the Pacific and Farallon

plates reached the subduction zone at the North American plate (Atwater, 1970; Furlong

and Schwartz, 2004, Mclaughlin et al., 1994). As the SAF and MTJ propagate northward,

the subducted Gorda plate moves northeastward beneath the North American plate

creating a slab window (Furlong et al., 1989). This slab window allows mantle material

to well up under the North American plate causing crustal deformation (Furlong and

Govers, 1999). This deformation is modeled as crustal thickening in advance of and

during the passage of the MTJ followed by thinning of the thickened crust in its wake,

called the Mendocino crustal conveyor (MCC) which results in a double-humped pattern of uplift (Furlong and Govers, 1999; Furlong and Schwartz, 2004; Lock et al., 2006). It is estimated that the MTJ migrates northward at the same rate as the relative Pacific-North

American plate motion, around 5 cm/yr (Atwater, 1970; Lock et al., 2006; Mclaughlin et

al., 1994; Merritts and Vincent, 1989) (Figure 3).

North of the MTJ, northwest striking fold and thrust belts are the result of

northeastward-directed compression from the Gorda plate subducting beneath North

America. Crustal shortening in this region has been estimated at a minimum of 13 mm/yr

with additional shortening from the growing Freshwater, South Bay and Eel River

synclines (Carver and Burke, 1992; Clarke and Carver, 1992; McCory, 2000). South of

the Eel River Syncline, uplift along the coast has been measured from marine terraces

and stream morphology. Uplift rates vary along the coast due to the position of the MTJ,

with the highest rates (4 mm/yr) occurring just south of Punta Gorda (Merritts and Bull,

89; Merritts and Vincent, 1989). Cape Mendocino is one of the most seismically active

locations in North America. Young tectonic activity suggests an active CSZ and

interplate coupling (Wang et al., 2001) that is sufficient to produce large (ca. M 9)

earthquakes. Three-dimensional plots of seismicity at the southern end of the CSZ show

evidence of a locked southern segment and define the southern edge of the Gorda plate

(Pryor and McPherson, 2006). Gaps in seismicity between the southern edge of the subducted Gorda plate and strike-slip events show evidence of the slab window and a locked northern SAF (Clarke and Carver, 1992; Furlong and Schwartz, 2004; McPherson et al., 2010).

METHODS

The headwaters region of the Mattole River has wide, shallow gradient valleys of river terraces preserved above the active channel by rock uplift and channel incision

(Figure 5). As the river evolves to keep its channel profile in equilibrium, the abandoned former valley bottoms provide insight into their formation (Whipple and Tucker, 2002).

Four tributaries: Baker Creek, Thompson Creek, Lost River and Ancestor Creek, were studied in order to examine terrace development in the headwater region of the Mattole

River (Figure 5). These sites were chosen for their accessibility and location in the drainage. Baker Creek has the easiest access and has the most data available, making it the best tributary to assess terrace stratigraphy, bedrock topography and date terrace sediments.

Geomorphic Mapping and Surveying

Topographic surveys were initially conducted prior to this study along reaches on two of the four tributaries of interest: Baker Creek and Lost River, in order to aid in projects designed to restore healthy fish habitat in bedrock channels by increasing sediment and groundwater storage. Topography was surveyed using an arbitrary datum using imperial measurement, so for the purpose of this study, all surveys were also measured in similar units. All analysis of terrace surveys were originally done in imperial units and then later converted to metric units for discussion. Topographic models in

Baker Creek were generated from these surveys and are also shown in imperial units.

Surveys were completed using a Sokkia set 5 total station and SDR33 data collector. The data were evaluated in AutoCAD to delineate breaklines, such as terrace risers, and generate an .XML file compatible with an available Geographic Information

System (GIS). The .XML file was imported into ArcGIS 10.1 and a Triangular Irregular

Network (TIN) modeled elevation surface was created (Figure 7). From the TIN surface, different Digital Elevation Models (DEMs), hillshades, and elevation contours were created in order to analyze the ground surface. Survey points in the arbitrary datum were tied into the NAD83 UTM Zone 10 datum using a handheld Garmin Etrex Legend H

GPS unit with data input into ArcGIS 10.1. These surveys covered a 1,070 m (3,500 ft) reach in Baker Creek, and a 460 m (1,500 ft) reach in Lost River, extending no more than

90 m (300 ft) from the active channel. In order to capture the most complete record of terrace surfaces in the headwater region of the Mattole River, additional surveys of much wider channel cross sections were conducted across all four tributary valleys.

Cross sections were surveyed using a Leica TPS 1100 with a RCS 1100 remote control system using an arbitrary datum measured in feet. Baker Creek, Lost River and

Ancestor Creek each have four surveys across the valleys; Thompson Creek has only two due to limited access (Figure 5). The surveys were conducted perpendicular to the active channel from valley wall to valley wall. The data was then imported into ArcGIS 10.2 and tied into the NAD83 UTM Zone 10 datum using a handheld Garmin Etrex Legend H

GPS unit. The profiles were then plotted in Excel and used in identifying terrace suites in each tributary (Figure 8).

Through field mapping and analysis of cross sections and topographic surveys,

terraces were delineated and assigned relative ages based on elevations above the active

stream channel, for each tributary. Terraces were digitally mapped in ArcGIS 10.2 for

Baker Creek where the most high-resolution elevation data made it possible. The highest

resolution data available online for the study area is 10 meters or 1/3 arc-second (USGS,

2013), which is comparable to the USGS 7.5 minute topographic contour data. Due to the lack of higher resolution data, terraces for the four tributaries were mapped along their

DEM-generated longitudinal profiles (discussed in the following DEM analysis section).

Auger Hole Data

Terrace stratigraphy and bedrock topography were gathered in Baker Creek through a series of hand dug auger holes and monitoring well data (Figure 7). Dry season water shortages have become a perennial problem, particularly in the upper reaches of the

Mattole River. Low flows impact water quality and supply, which have lead to considerable efforts to address water storage in the headwaters (MRRP, 2009). In Baker

Creek, wells (Figure 7) were installed in order to monitor how ground water levels respond to restoration efforts in the stream channel (well data provided by Sanctuary

Forest, 2015 personal communication). These wells along with several hand augured holes placed in this study, allowed me to describe terrace stratigraphy and estimate bedrock elevations. Each monitoring well and auger hole was excavated to bedrock, which ranged in depth from 1.4 m (4.5 ft) to 4.4 m (14.5 ft) from the surface, with the

19 exception of one site (NI W1 – Figure 7), where the depth of bedrock exceeded the maximum auger depth of 6 m (20ft).

To create a model for the bedrock topography in Baker Creek, elevations were calculated for all sites where depths to bedrock were measured. Topographic elevations were surveyed in feet and resulting depths to bedrock are plotted in feet. The active Baker

Creek channel is incised down to bedrock so all thalweg point elevations were also used as bedrock elevations. These bedrock elevation points were then combined in ArcGIS

10.2 to interpolate the surface and generate a DEM of the bedrock topography.

Optically Stimulated Luminescence Age Estimates

Absolute ages of some terraces in Baker Creek were determined using Optically

Stimulated Luminescence (OSL) dating. OSL dating estimates the last time sediments containing quartz or feldspar were exposed to sunlight. Sunlight resets the luminescence signal, so after burial, the signal grows over time from exposure to radioactive isotopes and cosmic rays (Gray et al., 2015; Mahan, written communication, 2015, see website http://gec.cr.usgs.gov/projects/lumlab/; Rittenour, 2008). Estimates for ages of terrace deposits in Baker Creek are from OSL dating on 180-90μ quartz grains using single aliquot analysis with blue LEDs. I conducted this analysis at the US Geological Survey

(USGS) Luminescence Geochronology Laboratory in Denver, Colorado under the supervision of USGS personnel, Shannon Mahan.

Samples for OSL analysis were collected from three different terraces in Baker

Creek: Terrace 2, Terrace 3 and Terrace 4 (Figure 7). For each sample site, three

20 sediment samples were taken from within a vertical profile within the terrace with the stratigraphically lowest sample directly above bedrock where possible (Figure 9). My assumption was that sediment collected near the bedrock contact would provide reasonable time constraint for when the stream was widening the valley and sediment sampled higher in the terrace would provide estimates for how long aggradation was occurring before being abandoned (Wegmann and Pazzaglia, 2002).

Sampling guidelines used in this study follow a 2015 USGS Information Handout by Shannon Mahan (U.S. Geological Survey Luminescence Dating Laboratory, Optically

Stimulated Luminescence (OSL) Sampling Instructions). In order to avoid errors from cosmic radiation, the samples were taken from under a black tarp, on a fresh, undisturbed exposure, at least 1 m below the top of the surface and a minimum of 0.5 m into a face of the deposit. The samples were collected using 7.6 cm diameter and 20 cm long opaque

PVC. Before inserting the sharpened end of the PVC tube into the exposure, a cap was placed on the other end and a plug was used to keep sediment from mixing as it was driven into the deposit by hand. Once the sample was fully inserted and completely packed, it was removed, plugged and capped closed, covered in aluminum foil and duct taped shut. The depth, elevation and latitude/longitude were labeled for use in determining cosmic contribution. Additional non light-sensitive bulk samples were collected in plastic bags from around the inside the sample holes for use in measuring water content and dose rates of the sediment. All samples were placed in a Styrofoam cooler and shipped to the OSL lab in Denver, Colorado.

For sample preparation in the lab, bulk samples were used to measure water

content and chemistry of the sediments to determine dose rates. Each sample was

extracted from the tubes under safe lighting conditions similar to a dark room using red

and amber light. The samples were placed in beakers and cleaned first with hydrochloric

acid (HCl) to remove carbonates and then with hydrogen peroxide (H2O2) to remove organic material. Each sample was wet sieved through a set of three sieves to produce two separate grain sizes for each sample. After drying, iron-bearing minerals were removed from the sieved samples using a Frantz magnetic separator. The size portion of the sample with the most grains, which in all cases for Baker Creek was the 180-90 μ size, was used for OSL analysis. Feldspars were then removed from the quartz by using heavy liquid separation; the higher density quartz sank to the bottom where it was frozen with liquid nitrogen and the feldspars in suspension were decanted out. The quartz was then thawed, filtered out of the liquid, rinsed with water and dried. Finally, the quartz was treated with hydrofluoric acid (HF) to remove any remaining feldspars and to etch the outer sides of the grains, before being loaded on to discs for analysis.

DEM Analysis

Longitudinal profiles (long profiles) of river channels are plots of distance along the thalweg vs. elevation. The long profile of a river is the product of the interaction between lithology, tectonics and climate and results in erosion or aggradation of the river channel. Disequilibrium between uplift and incision results in points of inflection

(knickpoints) in the long profile (Whipple and Tucker, 1999; Whittaker et al., 2008).

Fluvial terraces preserve the record of paleo-long profiles that have changed position over time with rock uplift and channel incision (Merritts et al., 1994; Pazzaglia et al., 1998).

Long profiles of the entire Mattole River and the four headwater tributaries of interest were generated from a 10m DEM in ArcGIS 10.2 (USGS, 2013). While flights of terraces along the main stem Mattole River cannot be precisely mapped without higher resolution elevation data such as LiDAR, a general sense of terrace height above the active channel can be observed in the valley longitudinal profile. The valley longitudinal profile is generated from distances and elevations of a line drawn through the center of the river valley, unlike the river longitudinal profile, which uses the thalweg. Due to the sinuosity of the Mattole River, the valley long profile is shorter than the river channel profile. In order to compare the two profiles, the sinuosity of the Mattole River thalweg was removed. This was done by plotting the elevation of the thalweg where it crosses the valley center line with respect to the valley center line distance (Figure 10). Although this method makes the Mattole River seem shorter overall, it allows the active channel profile to be compared to the paleo-long profiles recorded by terraces in the river valley.

RESULTS

Terraces and Relative Ages

I defined flights of terraces in Baker Creek, Thompson Creek, Lost River and

Ancestor Creek in the headwater region of the Mattole River (Figure 5, Figure 11, Table

1). Similar relative terrace ages were measured in Baker Creek, Thompson Creek and

Lost River with terrace surfaces occurring roughly 1.5 m, 2.1 m, 3 m, 4.6 m, 6.1 m and

9.1 m above the active stream channels. In Baker Creek, six terraces were identified up to

8.8 – 9.1 m above the thalweg; In Thompson Creek, six terraces were surveyed up to 8.8

– 9.1 m; six terraces were also in Lost River occurring up to 8.2 – 9.1 m above the active

channel thalweg. In Ancestor Creek, the most upstream of the four headwater tributaries

of interest, only three terrace surfaces were surveyed up to 2.7 – 3 m above the channel

(Table 1).

Figure 11. Terrace map of Baker Creek. Terraces mapped on high resolution topographic contours generated from survey data measured in feet and are shown in feet

Table 1. Terrace sequences in headwater tributaries from cross sectional surveys based on elevation above the active channel thalweg.

Tributary name Terrace number Elevation above active Elevation above active channel (feet) channel (meters) Baker Creek 1 <5 <1.5 2 6 – 8 1.8 – 2.4 3 10 3 4 14 – 16 4.3 – 4.9 5 20 – 21 6.1 – 6.4 6 29 – 30 8.8 – 9.1

Thompson Creek 1 <5 <1.5 2 6 – 7 1.8 – 2.4 3 10 – 12 3 – 3.7 4 13 – 15 4 – 4.6 5 20 – 21 6.1 – 6.4 6 29 – 30 8.8 – 9.1

Lost River 1 <5 <1.5 2 6 – 7 1.8 – 2.1 3 10 3 4 13 – 15 4 – 4.6 5 19 – 20 5.8 – 6.1 6 27 – 30 8.2 – 9.1

Ancestor Creek 1 <5 <1.5 2 7 – 8 2.1 – 2.4 3 10 3

Bedrock Topography and Terrace Stratigraphy

Terrace sediments in Baker Creek are comprised of units of silty sands with few

gravels and layers of sub-round to sub-angular clast-dominated gravels, not usually exceeding 6 cm (in diameter), interbedded with silts, clays, sands and lenses of rounded fine gravels and sands. In some places lenses of blue clays with variable amounts of sand and gravel can be found. Bedrock topography plotted vs. surface topography in feet as a result of survey datum (Figure 12). There appear to be at least two bedrock strath benches, where Baker Creek laterally cut across bedrock, which are also plotted in cross-

28 sections (Figure 12). Bedrock bench elevations are at 0.3-0.6 m and 1.5-3 m above the active channel thalweg.

Absolute Ages of Terraces

Three fluvial terraces, Terraces 2-4, were sampled in Baker Creek to estimate their age of deposition (Figure 7, Figure 9). Of the ten samples collected eight were acceptable to use for age estimates from OSL on 180-90 μ quartz grains using single aliquot analysis (Figure 13). Using OSL to estimate ages for sediments deposited in water can be challenging and lead to overestimation due to incomplete zeroing of the signal from poor light exposure in the channel. Improved procedures for OSL dating in recent years results in considerably less error, but all age estimates used in this study should be considered maximum ages (Mahan, 2007; Wallinga, 2002).

Sediments from Terrace 2 were collected from two site locations (Figure 11). At site BT2a samples were collected from a cut bank in Terrace 2 at two depths: BT2-1a from 1.4 m and BT2-2 from 1.9 m below the top of the terrace surface (Figure 9). The deeper sample, BT2-2, taken from a deposit of interbedded silty sands and sub-round gravels near the bedrock contact, yielded an age of 11,560 ± 840 years (Figure 13). The shallower sample, BT2a, gathered from a silty sand deposit with few rounded pebbles produced an age of 7,590± 390 years. Sample BT2b, collected from a deposit of silty sand with few rounded pebbles returned an age of 3,180 ± 190 years. BT2b was taken

Figure 13. Quartz OSL data and dates for Baker Creek, in the headwaters of the Mattole River, CA

just downstream of BT2a but is likely not representative of the terrace age due to

incomplete resetting of the luminescence signal or contamination while sampling.

Sample site BT4 is located on Terrace 4, roughly 100 feet from the channel

(Figure 11). Three samples were dated from a pit dug at this site: BT4-1 from 1.1 m,

BT4-2 from 1.5 m and BT4-3 from 1.8 m below the top of the terrace surface (Figure 9).

These samples were collected from lenses of silt and pebbles in a deposit of interbedded silty sands and sub-angular gravels, bedrock was not found at this site. The deepest deposit, BT4-3 produced the oldest age of 22,760 ± 1,640 years, up the section, BT4-2

was estimated to be 17,280 ± 1,140 years and BT4-1 produced an age of 17,030 ± 910

years (Figure 13).

Sediment from Terrace 3 was sampled from a cut bank (Figure 11) at two depths:

BT3-1 from 1.6 m and BT3-3 from 2.4 m (Figure 9). BT3-3 was taken from interbedded

silty sands and sub-round gravels near the bedrock contact and returned an age of 11,670

± 720 years. BT3-1 was collected from a silty sand deposit with few rounded pebbles and

produced an age of 8,360 ±460 years (Figure 13).

Longitudinal Profiles

Terrace elevations determined from geomorphic mapping and cross-sectional

surveys were plotted and projected along the long profiles of each of the tributaries

(Figure 14). Apparent steps in the detailed plots of long profiles in Thompson Creek, Lost

River and Ancestor Creek reflect the resolution of the DEM and not necessarily the

morphology of the stream.

Along the long profile of the Mattole River, two significant convexities occur 30-

40 km and 75-85 km upstream from the mouth (Figure 15). Additionally, two knickpoints

are present in the headwater region, located 107 km and 112 km upstream from the

mouth (Figure 16). Deviations of the valley center profile from the channel long profile allude to locations where extensive terrace preservation is occurring and the general height where they occur above the active channel. These differences in the valley canter line from the long profile, or areas of terrace preservation, occur along two sections of the profile: the first is from 0 km, at the mouth of the Mattole River, to 35 km, with the greatest deviations occurring at 15-35 km and the second located 80-90 km upstream.

A comparison of channel elevation relative to topographic height of the western

watershed boundary reveals three zones of high relief (Figure 15). Approximately 850 m of relief, occurs about 18 km upstream of the mouth, approximately 50 km upstream, the zone of greatest relief exists between King Peak and the Mattole River, equaling approximately 1000 m, and in the headwater region of the Mattole River, around 85 km upstream there is roughly 500 m of relief.

DISCUSSION

Fluvial Terrace Sequences

Changes in tectonic signal and climate are associated with changes in incision and aggradation in a river, recorded by fluvial terraces. Terraces are preserved by renewed incision of a river into its floodplain, as a response to relative base level lowering or a decrease in sediment supply (Merritts, 2007; Pazzaglia and Brandon, 2001; Personius,

1993; Schumm, 1993; Wegmann and Pazzaglia, 2009). Three headwater tributaries of the

Mattole River, Baker Creek, Thompson Creek and Lost River have each recorded six terrace surfaces abandoned equal heights above the active channel at roughly 1.5 m, 2.1 m, 3 m, 4.6 m, 6.1 m and 9.1 m. In Ancestor Creek, the furthest upstream tributary studied, only three terraces are preserved, these occurred at 1.5 m, 2.1-2.4 m and 3 m above the active channel (Table 1). In all cases, the first terrace, 1.5 m or less above the active channel likely represents the current floodplain, experiencing active erosion and deposition during high flows. As the Mattole River adjusts its long profile to accommodate crustal uplift and changes in climate related sediment loads, knickpoints or knickzones, points or zones of inflection in the profile, will propagate upstream through the main stem and it’s tributaries (Holbrook and Schumm, 1999; Howard, 1998; Miller et al., 2013). As knickpoints migrate through the headwater tributaries, flights of terraces are preserved above the incising channel. If similar flights of terraces are being recorded in different drainages in the headwaters region, it could mean that they have each

37 responded to similar signals. Baker Creek, Thompson Creek and Lost River have all recorded the same signal in flights of terraces, where Ancestor Creek has only recorded half of the terraces. The knickpoint in the headwaters located 107 km upstream from the

Mattole River has yet to migrate through the tributaries of interest, but as it does, slope adjustment resulting in incision will likely continue throughout the watershed. A knickpoint located 112 km upstream from the mouth of the Mattole River has eroded its way through Baker Creek, Thompson Creek and Lost River, further abandoning terraces above the active channel. This knickpoint has not yet reached Ancestor Creek and will lead to further incision of that tributary as it adjusts the channel slope upstream.

In Baker Creek, high-resolution topographic data and numerous monitoring wells and auger holes made it possible to map the flight of six terraces along the active channel as well as the position of the bedrock in the valley, providing thicknesses for Terraces 1 through 5 (Table 2). Bedrock strath bench positions and elevations at 0.3 to 0.6 m and 1.5 to 3 m above the active channel suggest that Terraces 2 and 3 are from the same valley widening/filling deposit, while Terraces 4 and 5, which occur at higher elevations and above the higher bedrock bench, are likely from the same, but older aggradation deposit.

Table 2. Terrace thickness and incision rates using OSL ages of sediments from Baker Creek

Terrace Elevation Elevation Thickness Thickness Bedrock Bedrock Age (ka) Incision number above above (feet) (meters) elevation elevation rate active active above above (m/ka) channel channel active active (feet) (meters) channel channel (feet) (meters) 2/3 6 – 10 1.8 – 3 4 – 9 1.2 – 2.7 1 – 2 0.3 – 0.6 11 – 8 0.38

4/5 14 – 21 4.3 – 6.4 9 – 16 2.7 – 4.9 5 – 10 1.5 – 3 >22 – 17 0.29

6 29+ 8.8+ ? ? ? ? >22 ?

Paleoclimate

Modern oceanic and atmospheric conditions in the northeastern Pacific Ocean

have a significant effect on the climate along the west coast of North America. Rivers are

sensitive to changes in climate, making terraces useful in unraveling the evolution of the

drainage basin (Merritts, 2007). Due to high sedimentation rates, sediments deposited

offshore of Northern California and Oregon are excellent recorders of changes in the late

Quaternary climate. High-resolution studies from Ocean Drilling Program (ODP)

sediment cores in this region use microfossils, pollen, calcium carbonate (CaCO3) and total organic carbon (Corg) to reconstruct millennial and even decadal scale changes in

oceanic conditions and continental climate (Barron et al., 2003; Heusser, 1998; Heusser,

Lyle and Mix, 2000; Lyle et al., 2000; Pisias, Mix and Heusser, 2001; Sabin and Pisias,

1996). Comparison of this record shows that shifts in Pacific Northwest climate over the

past glacial cycle are consistent with Greenland ice core data and North Atlantic sediment

records at least until the last 10 ka (Barron et al. 2003; Heusser, 1998; Pisias, Mix and

Heusser, 2001).

During the Last Glacial Maximum (LGM) in Northern California, around 20 ka, radiolarian assemblages were mostly cold water Bering Sea assemblages. Deglaciation is marked by decreases in this assemblage and an increase in Transitional and Eastern

Boundary Current (EBC) assemblages, which indicate a change into warmer waters and increased coastal upwelling (Mix et al., 1999; Pisias, Mix and Heusser, 2001; Sabin and

Pisias, 1996). In studies of pollen assemblages, changes in Sea Surface Temperatures

(SSTs) are related to changes in terrestrial vegetation. Deglaciations are marked by decreases in Pine and shrub assemblages, and increases in redwood and alder assemblages. The two contrasting vegetation types reflect significant differences in mean annual temperatures and precipitation. Alder is known for growing in disturbed environments and in moist redwood forests, which reflect a wetter climate with increased upwelling and associated fog drip (Heusser, 1998; Heusser et al. 2000). Studies of sediment composition note that laminated sediments and increases in accumulation rates of organic carbon and CaCO3 mark deglaciation intervals (Barron et al., 2003; Lyle et al.,

2000). Proxies for paleoclimate in the Pacific Northwest show similar trends in moisture

and temperature onshore. Pollen evidence suggest a warm, wet interval coming out of

LGM around 18 ka, peaks in upwelling and higher sedimentation rates in the microfossil

and organic carbon record occur during this time and around 13 ka, suggesting generally

wet climates until the Younger Dryas, a well documented return to near glacial conditions

around 12 ka. The Younger Dryas at 12 ka saw near glacial levels of Bering Sea

assemblages and an increase in pine during this time, immediately followed by

considerable warmer and wetter interval marked by a peaks in upwelling EBC

assemblages, in alder and redwood pollen and organic carbon between 11 – 8 ka. 8 ka

reflects maximum temperatures and establishment of vegetation similar to modern forests

(Barron et al., 2003; Heusser, 1998; Heusser, Lyle and Mix, 2000; Lyle et al., 2000;

Mann and Hamilton, 1995; Mix et al., 1999; Pisias, Mix and Heusser, 2001; Sabin and

Pisias, 1996).

Late Pleistocene Holocene Terrace Formation

For Baker Creek, the number of terraces, their elevations, and their ages can be correlated to changes in paleoclimate and ongoing tectonic uplift. Increased sediment loads caused by changes in climate would result in aggradation of river sediments whereas a decrease in sediment would result in incision of the river channel. Continued channel incision and rock uplift cause the abandoned terrace surfaces to rise above the active channel where they are preserved in the valley sides (Merritts, 2007; Pazzaglia and

Brandon, 2001; Personius, 1993; Schumm, 1993; Wegmann and Pazzaglia, 2009).

Climate models for the last glacial –interglacial cycle indicate warm, wet intervals and increased sedimentation rates offshore, occur after LGM, around 18 ka, 13ka and from

11-8 ka. (Barron et al., 2003; Heusser, 1998; Heusser, et al., 2000; Lyle et al., 2000;

Mann and Hamilton, 1995; Mix et al., 1999; Pisias et al., 2001; Sabin and Pisias, 1996).

Elevations and absolute ages of terraces in Baker Creek correspond to two valley widening/fill intervals, terraces 4 and 5 correlate to the warm, wet interval around 18 ka

with aggradation occurring after LGM to 17 ka and Terraces 2 and 3 correlate to the

warm wet interval occurring after the Younger Dryas with aggradation occurring from 11

– 8 ka (Figure 17). Using the thicknesses of Terraces 5 and 3, incision rates were calculated for 17 to 11 ka and 8 ka to present, as 0.27 m/ka and 0.38 m/ka, respectively

(Table 2).

Terrace Formation Model

I propose a model of how and when terrace formation might have occurred in

Baker Creek. This may be applied to the general lower headwater region of the Mattole

River, where at least two other tributaries, Thompson Creek and Lost River have recorded similar terrace flights (Figure 18a). The higher bedrock strath bench in Baker

Creek is more defined in the upper parts of the surveyed reach. Bedrock elevations were not measured in any of the other tributaries, therefore a second model is proposed without bedrock elevation constraints (Figure 18b).

Regardless of the position of the highest bedrock strath bench, there must have been valley aggradation up to 17 ka, when Terrace 5 was abandoned. The cold Younger

Dryas interval would have resulted in decreased sediment load and valley incision down to bedrock until 11 ka, when Terrace 4 was cut into Terrace 5 sediments (Figure 18). At

11 ka bedrock was beveled and the valley filled again until 8 ka when Terrace 3 was abandoned. 8 ka marks a drier climate leading to present day conditions, which would have resulted in reduced sedimentation causing incision and the cutting of Terrace 2 into

Terrace 3 sediments. This model correlates with ages determined by OSL of terrace sediments of Terrace 2 and 3, which returned equivalent ages for sediments from both terraces (Figure 13).

Relation of Mattole River to MTJ Region

Drainage basins in northwestern California have been adjusting to crustal deformation and surface uplift associated with the northward migration of the MTJ throughout the Quaternary (Merritts, 1996). Fluvial terraces and longitudinal profiles of rivers record the evolution of drainage basins. As a river responds to changes in equilibrium, specific patterns in its channel profile can be used to interpret changes in tectonic and climate signals (Barron et al., 2003; Hancock and Anderson, 2002; Merritts,

2007; Merritts and Vincent, 1989; Merritts et al., 1994; Pazzaglia and Brandon, 2001;

Pazzaglia et al., 1998; Personius, 1995; Wegmann and Pazzaglia, 1998).

I interpret convexities in the long profile of the Mattole River to be the channel’s adjustment to tectonic forcing and crustal deformation. Typical long profiles of rivers, said to be in equilibrium with rock uplift and erosion, commonly exhibit an inverse power-law relation between drainage area and slope, where the steepest slopes occur in the headwaters, and decrease downstream as drainage area increases (Holbrook and

Schumm, 1999; Miller et al., 2013; Pazzaglia et al., 1998). In order for the Mattole River to reach such an equilibrium profile as it flows north through areas of significant crustal deformation and rock uplift, the river would have to adjust its channel slopes upstream and downstream of the uplifted zone by aggrading and incising through the zone (Figure

19 from Holbrook and Schumm, 1999)

Comparison of the long profile of the Mattole River to the valley center line

profile identifies regions where incision has adjusted the channel profile and preserved

terraces, recording positions of its former valley bottom. Terrace preservation in the

Mattole River occurs primarily in two areas on the Mattole River at 15-35 km and at 80-

90 km upstream from the river mouth. These two areas of terrace preservation are located immediately upstream and downstream of the two major convexities in the Mattole long profile (Figure 15). In contrast to the typical stream profile with steep, boulder-laden headwaters, the Mattole River headwater region has decreased gradient with a relatively broad alluvial plain consisting of strath and fill terraces (Figure 5) This is in response to transient passage of uplift due to thickened crust associated with the migration of the

MTJ, resulting in higher rates of uplift in the middle of the Mattole River. The changes in gradient and terrace character also reflect differences in sediment inputs, due to

47 changes in climate, to be recorded where typical headwater steep gradients and low velocities would have otherwise not formed a floodplain (Kirby and Whipple, 2012;

Merritts et al., 1994).

Comparison of the long and valley center profiles of the Mattole River with the topographic profile of the watershed’s western boundary, defines three zones of high relief that appear to be coordinated to the profile of the river (Figure 15). Topographic relief between the western boundary profile and the long profile of the Mattole River, suggest that the zones of highest uplift coincide with river incision. The northernmost location of convexity in the long profile (at 30 to 40 km from the river mouth) corresponds to the highest zone of relief between Kings Peak and the Mattole River.

Studies of marine terraces and coastal drainages in the King Range have comparable results for patterns of uplift before and after the passage of the MTJ (Merritts and

Vincent, 1989; Merritts et al., 1994; Pazzaglia et al., 1998). Crustal thickening and subsequent thinning predicted by the MCC, determined from studies of landforms inland of the study site, suggests a double “humped” pattern of uplift, driving rock uplift and subsidence in the wake of the MTJ as it migrates northwestward (Furlong and Govers,

1999; Furlong and Schwartz, 2004; Lock et al., 2006). While the two uplift patterns cover vastly different distances, they show similar locations of high rates of uplift. Presently, the highest rates of uplift along the coast, ca. 4m/ka, are between Randall Creek (marine terrace site C, Figure 1) and Big Flat (Merritts and Bull, 1989) which correspond with the northernmost convexity in the Mattole River long profile as well as the zone of highest relief (Figure 20). This location of crustal deformation and rock uplift, located along the

48 middle portion of the Mattole River, also corresponds to the northernmost peak in uplift associated with slab window crustal thickening predicted by the MCC (Lock et al., 2006)

(Figure 20). Both models also show that after a peak in uplift, reduced uplift rates results in regional tilt (Merritts and Vincent, 1989), and crustal thinning (Furlong and Govers,

1999; Lock et al., 2006).

Converse to the middle course of the Mattole River where coastal uplift rates are about 4m/ka, the headwaters are located in the area of reduced uplift rates, measured by

Merritts (1989) along the coast, at a rate of about 1m/ka. Incision rates measured by terrace elevations and ages in Baker Creek in this study suggest a third of that rate (0.3 m/ka) have occurred since 8 ka. While these rates are not the same, it seems reasonable that uplift rates would be reduced away from the coast and east of the King Range. Age estimates of sediments sampled in Baker Creek, used for calculating incision rates (Table

2), are maximum ages of terrace abandonment. Terrace and bedrock elevations used to determine terrace thickness resulted in a range of thickness, where the thickest height was used for calculations of incision rates. Therefore rates calculated are maximum incision rates.

CONCLUSIONS

As the MTJ migrates northwestward, magma upwelling and viscous coupling

associated with the growth of a slab window underneath the North American plate, cause

rock uplift and crustal deformation. Uplift patterns associated with the passage of the

MTJ can be observed along the coast in uplifted marine terraces and coastal stream

geomorphology, as well as drainage patterns further inland. Peaks in rates of uplift and

crustal deformation modeled by Merritts and Vincent (1989) and Lock et al., (2006)

(Figure 3a,b) capture different scales of the deformation associated with the migration of

the MTJ and approximately correspond to locations of uplift and geomorphic features

seen in the Mattole River watershed (Figure 20). Uplift rates measured at the coast along the Mattole River are highest (4 m/ka) along the mid course of the river and decrease (1

m/ka) to the south (west of the headwaters). Uplift also diffuses east of the King Range

by about one third, measured at about 0.3 m/ka in the headwaters (Table 2), compared to

1 m/ka at the coast. Differential rates of uplift along the length of the Mattole River have

lead to relatively low gradients in the headwater region (Figure 15). Climate induced

changes in sediment loads and discharge since the LGM, in combination with low

gradient stream channels, resulted in the formation of terraces in the headwater region of

the Mattole River. Age estimates of sediments in Baker Creek, suggest the timing of

valley widening and filling occurred after the LGM to 17 ka and from 11 to 8 ka which correspond to relatively warm and wet climate intervals seen in climate proxies in offshore sediment cores (Figure 17). Similar flights of terraces in three of the four

measured tributaries in the headwaters of the Mattole River, along with locations of small

knickpoints in the long profile (Figure 16), suggest that the river channel is actively adjusting its profile to accommodate drier climates and the transient passage of the MTJ.

REFERENCES

Atwater, T., 1970, Implications of plate tectonics for the Cenozoic tectonic evolution of western North America, Geological Society of America Bulletin, 81: 3513-3536.

Barron, J. A., L. Heusser, T. Herbert, and M. Lyle, 2003, High-resolution climatic evolution of coastal northern California during the past 16,000 years, Paleoceanography, 18(1), 1020

Bryant, W. A. (compiler), 2005, Digital Database of Quaternary and Younger Faults from the Fault Activity Map of California, version 2.0: California Geological Survey Web Page, http://www.consrv.ca.gov/CGS/information/publications/QuaternaryFaults_ver2.h tm; (2015)

Carver, G. A. and Burke R. M., 1992, Late Cenozoic Deformation on the Cascadia Subduction Zone in the Region of the Mendocino Triple Junction, in Carver, G.A., and Burke, R.M., eds., Pacific Cell, Friends of the Pleistocene Guidebook for the Field Trip to Northern Coastal California: Arcata, CA, p. 31-63

Clarke, S.H., Jr., and Carver, G.A., 1992, Late Holocene tectonics and paleoseismicity, southern Cascadia subduction zone: Science, v. 255, p. 188-192.

Coates, D.A., W. Hobson, B. McFadin, And C. Wilder, 2002, Mattole River Watershed Technical Support Document for the TMDLs For Sediment And Temperature. Draft for Public Review. California Regional Water Quality Control Board, North Coast Region.

Davenport, C. W., Thornburg, J., Delattre, M. P., Haydon, W. D., and Curless, J. M., 2002, Report on the geologic and geomorphic characteristics of the Mattole River watershed, California. Department of Conservation, California Geological Survey

Dimitru, T. A., 1991, Major Quaternary uplift along the northernmost San Andreas fault, King Range, northwestern California. Geology 19: 526-529

Furlong, K.P., and Govers, R., 1999, Ephemeral crustal thickening at a triple junction: The Mendocino Crustal Conveyor, Geology, v. 27, no. 2, p. 127-130.

Furlong, K.P., and Schwartz, S.Y., 2004, Influence of the Mendocino triple junction on the tectonics of coastal California: Annual Review of Earth and Planetary Sciences, v. 32 p. 403-433.

Furlong, K.P., Hugo, W.D., and G. Zandt, 1989, Geometry and Evolution of the San Andreas Fault Zone in Northern California, Journal of Geophysical Research, vol. 94, p. 3100 - 3110.

Gray, H.J., Mahan, S.A., Rittenour, T., and Nelson, M., 2015, Guide to luminescence dating techniques and their applications for paleoseismic research, proceeding in Lund, W.R., editor, 2015, Proceedings volume, Basin and Range Province Seismic Hazards Summit III: Utah Geological Survey Miscellaneous Publication 15-5, variously paginated

Hancock, G. S., and Anderson, R. S., 2002, Numerical modeling of fluvial strath-terrace formation in response to oscillating climate, Geological Society of America Bulletin 114, 1131–1142.

Heusser, L. 1998. Direct correlation of millenial-scale changes in western North American vegetation and climate with changes in the California Current system over the past ~60 kyr. Paleoceanography 13: 252-262.

Heusser, L. E., M. Lyle, and A. Mix. 2000. Vegetation and climate of the northwest coast of North America during the last 500 k.y.: high-resolution pollen evidence from the northern California margin. Pages 217-226 in M. Lyle, I. Koizumi, C. Richter and T. C. Moore, Jr., editors. Proceedings of the ocean drilling program, scientific results, Volume 167. Ocean Drilling Program, College Station, Texas.

Holbrook, J., and Schumm, S. A., 1999, Geomorphic and sedimentary response of rivers to tectonic deformation: a brief review and critique of a tool for recognizing subtle epeirogenic deformation in modern and ancient settings. Tectonophysics 305: 287-306

Howard, A. D. 1998. Long profile development of bedrock channels: interaction of weathering, mass wasting, bed erosion, and sediment transport. Pages 297-319 in K. J. Tinkler and E. E. Wohl, editors. Rivers over rock: fluvial processes in bedrock channels. Geophysical Monograph 107. American Geophysical Union, Washington, D. C.

Kirby, E., and Whipple, K. X., 2012, Expression of active tectonics in erosional landscapes. Journal of Structural Geology 44: 55-75

Koehler, R.D., 1999, Terrace Formation, Drainage Adjustment and Tectonic Geomorphology of the Van Duzen/North Fork Eel Rivers Headwater Region, Northern California, [master’s thesis]: Humboldt State University.

Lajoie, K.R., Sarna-Wojcicki, A.M., and Ota, Yuko, 1982, Emergent Holocene marine terraces at Ventura and Cape Mendocino, California – indicators of high tectonic uplift rates [abs.]: Geological Society of America Abstracts with Programs, v., 14, no. 4, p. 178

Lock, J., Kelsey, H., Furlong, K., Woolace, A., 2006, Late Neogene and Quaternary landscape evolution of the northern California Coast Ranges: Evidence for Mendocino triple junction tectonics: GSA Bulletin, v. 118; no. 9/10, p. 1232- 1246.

Lyle, M., I. Koizumi, M. L. Delaney, and J. A. Barron. 2000. Sedimentary record of the California Current system, middle Miocene to Holocene: a synthesis of Leg 167 results. Pages 341-376 in M. Lyle, I. Koizumi, C. Richter and T. C. Moore, Jr., editors. Proceedings of the ocean drilling program, scientific results, Volume 167. Ocean Drilling Program, College Station, Texas

Mahan, S. A., 2007, Late Quaternary stratigraphy and luminescence geochronology of the northeastern Mojave Desert. Quaternary International 166: 61-78

Mahan, S. A., 2015, U.S. Geological Survey Luminescence Dating Laboratory, Optically Stimulated Luminescence (OSL) Sampling Instructions. USGS Information Handout, http://gec.cr.usgs.gov/projects/lumlab/docs/USGS-OSL-sampling- instructions-508.pdf

Mann, D. H., and Hamilton, T. D., 1995, Late Pleistocene and Holocene Paleoenvironments of the North Pacific Coast. Quaternary Science Reviews 14: 449-471

McCrory, P. A., 2000. Upper plate contraction north of the migrating Mendocino triple junction, northern California: implications for strain partitioning. Tectonics 19, 1144-1160.

McLaughlin, R.J., Ellen, S.D., Blake, M.C., Jayko, A.S., Irwin, W.P., Aalto, K.R., Carver, G.A., and Clark, S.H.; 2000, Geology of the Cape Mendocino, Eureka, Garberville, and southwestern part of the Hayfork – 30x60 minute Quadrangles and Adjacent Offshore Area, Northern California, U.S. Geological Survey, Miscellaneous Field Study 2336, 1:100,000.

McLaughlin, R.J., Sliter, W.V., Frederikson, N.O., Harbert, W.P., and McCulloch, D.S., 1994, Plate motions recorded in tectonostratigraphic terranes of the Franciscan Complex and evolution of the Mendocino triple junction, northwestern California: U.S. Geological Survey Bulletin 1997, p. 60

McPherson, B. C., Hemphill-Haley, M., Pryor, I., Greger, D., Hellweg, P., and Rollins, C., 2010 Geodetic and seismologic evidence for a locked Southern margin of the Cascadia Subduction Zone, Poster presented at the Seismological Society of America Annual Meeting

Merritts, D. J., 1996, The Mendocino triple junction: Active faults, episodic coastal emergence, and rapid uplift, Journal of Geophysical Research, 101(B3): 6051- 6070

Merritts, D. J., 2007, Fluvial Environments: Terrace Sequences. Encyclopedia of Quaternary science 1: 694-704

Merritts, D.J., and W.B. Bull, 1989, Interpreting Quaternary uplift rates at the Mendocino triple junction, northern California, from uplifted marine terraces, Geology, v. 17, p. 1020-1024.

Merritts, Dorothy, and Vincent, K.R., 1989, Geomorphic response of coastal streams to low, intermediate, and high rates of uplift, Mendocino triple junction region, northern California: Geological Society of America Bulletin, v. 100, p. 1,373- 1,388.

Merritts, D. J., K. R. Vincent, and E. E. Wohl. 1994. Long river profiles, tectonism, and eustasy: a guide to interpreting fluvial terraces. Journal of Geophysical Research 99: 14,031-14,050.

Miller, S.R., Sak, P.B., Kirby E., Bierman, P.R., 2013 Neogene rejuvenation of central Appalachian topography: Evidence for differential rock uplift from stream profiles and erosion rates, Earth and Planetary Science Letters, v. 369–370, p. 1- 12.

Mix, A. C., Lund, D. C., Pisias, N. G., Bodén, P., Bornmalm, L., Lyle, M., and Pike, J.,1999 Rapid climate oscillations in the Northeast Pacific during the last deglaciation reflect Northern and Southern hemisphere sources. Mechanisms of Global Climate Change at Millennial Time Scales 112: 127-148

Mattole River and Range Partnership (MRRP): Mattole Restoration Council, Mattole Salmon Group and Sanctuary Forest, 2009. Mattole Integrated Coastal Watershed Plan: Foresight 2020

Pazzaglia, F. J., and M. T. Brandon. 2001. A fluvial record of long-term steady-state uplift and erosion across the Cascadia forearc high, western Washington State. American Journal of Science 301: 385-431.

Pazzaglia, F. J., T. W. Gardner, and D. J. Merritts. 1998. Bedrock fluvial incision and longitudinal profile development over geologic time scales determined by fluvial terraces. Pages 207-235 in K. J. Tinkler and E. E. Wohl, editors. Rivers over rock: fluvial processes in bedrock channels. Geophysical Monograph 107. American Geophysical Union, Washington, D. C.

Personius, S.F. 1993, Age and Origin of Fluvial Terraces in the Central Coast Range, Western Oregon, U.S. Geological Survey Bulletin 2038.

Personius, S. F. 1995. Late Quaternary stream incision and uplift in the forearc of the Cascadia subduction zone, western Oregon. Journal of Geophysical Research 100: 20,193-20,210.

Pisias, N. G., A. C. Mix, and L. Heusser. 2001. Millenial scale climate variability of the northeast Pacific Ocean and northwest North America based on radiolaria and pollen. Quaternary Science Reviews 20: 1561-1576.

Prentice, C. S., D. J. Merritts, E. Beutner, E Bodin, A. Schill, and J. Muller. 1999. The northern San Andreas Fault near Shelter Cove, California, Geological Society of America Bulletin 111, 512-523.

Pryor, I., B, McPherson. 2006. Seismicity and stress near the Mendocino Triple Junction in Pacific Cell, Friends of the Pleistocene guidebook for the field trip to northern coastal California p. 16-27

Rittenour, T. M. 2008 (November): Luminescence dating of fluvial deposits: applications to geomorphic, paleoseismic and archaeological research. Boreas 37: 613–635.

Sabin, A. L., and Pisias, N. G., 1996. Sea surface temperature changes in the Northeastern Pacific Ocean during the past 20,000 years and their relationship to climate change in Northwestern North America. Quaternary Research 46: 48-61

Sanctuary Forest Inc., and Mattole Flow Program 2014. Mattole Headwaters Groundwater Management Plan

Schumm, S. A. 1993. River response to baselevel change: implications for sequence stratigraphy. The Journal of Geology 101: 279-294

Stallman, J.D., 2003. Strath Terrace Genesis in the North Fork Elk River Valley, North Coastal California, [master’s thesis]: Humboldt State University.

Wang. K., Mulder, T., Rogers, G. C., and Hyndman, R. D., 1995. Case for very low coupling stress on the Cascadia subduction fault. Journal of Geophysical Research 100: 12,907-12,918

Wegmann, K. W., and F. J. Pazzaglia. 2002. Holocene strath terraces, climate change, and active tectonics: the Clearwater River basin, Olympic Peninsula, Washington State. Geological Society of America Bulletin 114: 731-744.

Whipple, K. X., and G. E. Tucker. 1999. Dynamics of the stream-power incision model: implication for height limits of mountain ranges, landscape response timescales, and research needs. Journal of Geophysical Research 104: 17,661-17,674.

Whittaker, A. C., Attal, M., Cowie, P. A., Tucker, G. E., and Roberts, G., 2008. Decoding temporal and spatial patterns of fault uplift using transient river long profiles. Geomorphology 100: 506-526

U.S. Geological Survey, 2013. USGS National Elevation Dataset (NED) n41w125, n41w124, n40w125, n40w124, 1/3 arc-second 2013 1 x 1 degree ArcGrid: U.S. Geological Survey: Reston, VA, http://ned.usgs.gov/, http://nationalmap.gov/viewer.html.

APPENDIX

List of Abbreviations:

A - Alder

CSZ – Cascadia subduction zone

DEM – Digital Elevation Model

EBC – Eastern Boundary Current microfossil assemblage

GIS – Geographic Information System

GPS – Global Positioning System

HW – Headwaters

LED – Light Emitting Diode

LGM – Last Glacial Maximum

MCC – Mendocino crustal conveyor

MFZ – Mendocino fracture zone

MRFZ – Mad River fault zone

MTJ – Mendocino triple junction

NAD83 – North American Datum of 1983

NED _ National Elevation Dataset

ODP – Ocean Drilling Program

OSL – Optically Stimulated Luminescence

PVC – Polyvinyl chloride

RW - Redwood

SAF – San Andreas fault

SST – Sea Surface Temperature

TIN – Triangular Irregular Network

USGS – United States Geological Survey

UTM – Universal Transverse Mercator

VE – Vertical exaggeration