Assessment Components


The Mattole Basin has a Mediterranean climate characterized by cool wet winters with high runoff, and dry warm summers with greatly reduced flows. Most precipitation falls as rain. Along the coast, average air temperatures range from 46 to 56°F. Further inland, annual air temperatures are much more varied, ranging from below freezing in winter to over 100°F in summer. The Mattole Basin receives one of the highest annual amounts of rainfall in California, averaging 81 inches. Average rainfall near the coast in Petrolia is about 60 inches per year and well over 100 inches per year falls near the center of the basin in Honeydew. Extreme rain events do occur, e.g. over 240 inches fell over parts of the basin during 1982-83.

Water Quality

The Mattole River has been placed on a list of water bodies for impairment or the threat of impairment by sediment and temperature as required by Section 303(d) of the Clean Water Act. The 303(d) list describes water bodies that do not fully support all beneficial uses or are not meeting water quality objectives, and the pollutants for each water body that impair beneficial use and water quality. The listing of the Mattole River will eventually result in numeric targets for sediment and temperature allocations being developed by the North Coast Regional Water Quality Control Board (Regional Board) that are expressed as a total maximum daily load (TMDL) for each pollutant. At the time of the listing sediment and temperature were judged to be impacting the cold (COLD) water fishery and associated beneficial uses, described in the Water Quality Control Plan, North Coast Region, Region 1 (Basin Plan, 1996). Nearly all aspects of the cold water fishery are presumed affected by sediment and temperature pollution, including the migration, spawning and reproduction, and early development of cold water fish such as coho and Chinook salmon, and steelhead trout.

Other beneficial uses of water in the Basin Plan for the Mattole River include municipal, agricultural, industrial, water contact and non-contact recreation, commercial and sport fishing, wildlife habitat and those plant and animal populations associated with terrestrial ecosystems, as well as similar attributes in estuarine ecosystems. Aquaculture in the Mattole River is also foreseen as a potential beneficial use in the Basin Plan.

The Basin Plan also describes specific water quality objectives for the Mattole River that include limitations for in stream specific conductance, total dissolved solids, dissolved oxygen, and pH or hydrogen ion concentration. If exceedences to specific water quality objectives are discovered during NCWAP data gathering, collection, and analysis they will be elucidated and addressed in pertinent report sections. It should be noted that data was not available or not analyzed for all the Basin Plan objectives.


Mattole Bedrock Map
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Bedrock underlying much of the basin has been tectonically broken and sheared making it relatively weak, easily weathered, and inherently susceptible to landsliding and erosion. The unstable bedrock and soil conditions combined with heavy rainfall, high regional uplift rates, and seismicity produce widespread landsliding and large volumes of sediment input to streams. The geologic unit and/or landslide type present can affect the nearby sediment load (i.e., coarse versus fine-grained). The following provides a brief description of the basin geology and related landslide processes. Detailed discussions of the basin geology, associated mass wasting processes and land use issues are provided in the Geology Appendix A, along with 1:24,000 scale maps illustrating spatial distributions of the geologic units and mass wasting features.

The Mattole Basin is situated in a geologically complex and tectonically active area, with some of the highest rates of crustal deformation, surface uplift, and seismic activity in North America (Merritts, 1996). Basement rocks, assigned to the Coastal belt and Central belt of the Franciscan Complex by Irwin (1960) are predominantly structurally deformed marine sedimentary rocks (McLaughlin and others, 1982, 1983, 1994). The Coastal belt has been divided into three pervasively folded, sheared, and otherwise tectonically-disrupted terranes; from northeast to southwest, separated by generally northwest-trending shear zones, are the Yager, Coastal, and King Range terranes (McLaughlin and others, 1997). Late Cenozoic marine and non-marine deposits (Wildcat Group or equivalent) underlie a limited area of the watershed west and northwest of Petrolia. Quaternary alluvial deposits cover the bedrock along streambeds in the lower reaches of some tributaries and mainstem Mattole River, while remnants of older surficial deposits are locally preserved on elevated fluvial terraces in some valley areas and on wave-cut terraces along the coast.

The bedrock map units have been consolidated into three groups, herein referred to as hard, moderate, and soft geomorphic terrains. Specifically, the bedrock map units have been grouped into geomorphic terrains as follows:

Soft Terrain – Geologic subunits identified as having the greatest landslide density (cm1, serpentinite, and co1 on Plate 1, geologic report).

Moderate Terrain – Geologic subunits identified as having intermediate landslide density (y1, co2, and krk1), along with the small units of different lithology (e.g., cols, krb) which collectively underlie less than 1% of the study area.

Hard Terrain – Geologic subunits identified as having the lowest landslide density (y2, y3, co3, co4, krk2, and krk3).

The unconsolidated Quaternary deposits mapped overlying the bedrock are grouped together as a fourth geomorphic terrain. These terrains show a strong correlation with mapped landslide occurrence and type, and provide a simplified division of the watershed based on geology and landform that is useful in the analysis of other spatial data.


The Mattole Basin lies within the Cape Mendocino Hydrographic Unit, a subunit of the Eel River Hydrographic Area as described by the Department of Water Resources in Bulletin Series 94-8. The Mattole River Hydrographic Unit Code: 18010107 as described by the United States Geologic Survey (USGS). The Department of Water Resources (DWR), Statewide Planning Program delineates the Mattole Basin within the North Coast Hydrologic Region (HR), the Coastal (#03) Planning Subarea (PSA), and the Mattole-Bear (#27) Detailed Analysis Unit (DAU).

Winter monthly stream flows in the Mattole River measured near Petrolia average between 1,710 and 4,170 cubic feet per second (cfs). However, peak flows measured on December 22, 1955 and December 22, 1964 were 90,400 and 78,500 respectively. Bank full discharge at Petrolia occurs at approximately 31,000 cfs. “Summer and fall flows drop below 60 cfs, with a minimum measured flow of 15 cfs” (Department of Water Resources).

High seasonal rainfall on bedrock and other geologic units with relatively low permeability and steep slopes contribute to the very flashy nature of the Mattole’s watersheds. In addition, the runoff rate has been increased by extensive road systems and other land uses. High seasonal rainfall combined with a rapid runoff rate on unstable soils delivers large amounts of sediments to the river. As a result, the Mattole River transports a very high sediment load. This sediment is deposited throughout the lower gradient reaches as it is transported downstream through the system.

Diversions, Dams, and Power Generation
There are 50 licensed, permitted, or pending water rights within the Mattole Basin. This number does not include riparian users and other diversions that are not registered with the State Division of Water Rights (State Water Resources Control Board, 2001). No major dams or power generating facilities are located within the Mattole Basin.

Fluvial Geomorphology

The Mattole Basin contains about 692 miles of blue-line streams (CGS Geologic Report-Table 10). The blue-line streams were chosen because they are a consistent depiction of the major streams within the network and include perennial, ephemeral, and intermittent streams. The river system within the Mattole Basin is arranged in a contorted or irregular drainage pattern. The mainstem of the Mattole River flows in a general northwesterly direction, parallel to the structural grain of the Franciscan Complex. Tributaries to the mainstem flow generally to the northeast or southwest, perpendicular to the Mattole River, and often the larger tributaries branch upstream into channels that trend parallel to the mainstem.

The spatial distribution of source, transport, and response reaches governs the distribution of potential impacts and recovery times for the stream system. Channel slope was used to classify stream sections as source (>20%), transport (4-20%) or response (<4%) reaches. Streams with gradients greater than 20 percent are considered source areas for sediment, while those with gradients less than four percent are considered areas of sediment deposition (Montgomery and Buffington, 1997). The figure below shows the distribution of these slope classes for the Mattole Basin study area.

The areas of greatest susceptibility to sediment deposition are those where higher gradient reaches transition into low gradient reaches. For example, a given transport reach could have high velocity and streamflow, resulting in a large carrying capacity for sediment. If the gradient changes to a slow moving response reach, sediment can rapidly fall out and deposit in the channel or along the banks. Examples of this phenomenon can be found at major slope breaks along Lower and Upper North Forks of the Mattole River. A specific example is shown in CGS Geologic Report-Figure 22, which is a photograph showing a tributary fan at the confluence of Conklin Creek and the mainstem Mattole River. Response reaches are found primarily in the Quaternary alluvium; these are reaches where sedimentation is most likely to occur.


Prior to European settlement, coniferous forest extended throughout most of the 190,000 acre Mattole Basin. Natural prairie grassland is concentrated on the northwestern portion of the basin, but prairie soils occur throughout the basin, mostly on ridgetops. The structural attributes, seral stages, and mix of species on the forestlands are determined by a combination of physical, biological, and disturbance factors. Physical factors include soil, moisture, temperature, and topography. The Mattole Basin is unusual within the Northern California coast as having very little redwood forest present; it is thought to be primarily due to the King Range blocking the summer fog. The interaction between soil types and strong salt-laden air are also possible factors that influence the redwood free areas of much of the Mattole and Bear River basins (Zinke, 1996). Forested stands consist primarily of tan-oak and Douglas-fir as the major tree species. Madrone, big-leaf maple, chinquapin, bay, canyon live-oak, and alder occur as minor components whose occurrence generally varies according to soil type, slope, and aspect controlling summer moisture regimes. Seral stages are dependent upon disturbance regimes, both natural and human induced. Natural disturbance includes fire started by lightning. Other coniferous species include yew, isolated sugar pine stands, and redwood in the southern headwaters.

The current vegetation is predominately forestland. Mixed conifer and hardwood forestland occupy 57% of the watershed while hardwood forests occupy 17% and coniferous forests occupy another 8%. Annual grasslands occupy 15% of the watershed. All other vegetation types occupy the remaining three percent of the watershed. With the exception of the estuary and areas where the river broadens out, there are no lakes or other reservoirs of significant size. Half of the watershed is covered by trees that have an average size of 12-24 inches diameter at breast height (dbh). Twenty percent of the area is covered by stands that average greater than 24-inch dbh trees and another 11% is covered by pole-sized trees 6-11 inches dbh.

Vegetation age classes in the Mattole Basin are quite young except for the scattered remaining un-entered old-growth stands. These are in protected status where they are in public ownership. The last stands of old growth in the Northern Subbasin are in private ownership and timber-harvesting plans there are invariably controversial. The previous harvest and grazing activities moved most stands to an earlier successional stage and consequently, hardwoods are now a part of the dominant canopy cover. However, it is clear from aerial photographs from the 1940s that hardwood was a major stand component. Early harvesting activities had a splotchy appearance from small stands and corners being left entirely un-entered and other areas having the appearance of an over-story removal, which left a substantial amount of vegetation in place. Other areas that are classified as forestland have a low level of livestock grazing. The size and location of mapped grasslands has also changed in response to past activities. Many of the existing grasslands are being encroached by woody vegetation. Studies cited in the draft Redwood Creek Watershed Analysis (RNSP 1999) suggest a number of causes including a climatic shift towards the currently cooler and moister climate about 2500 to 2800 years ago (West 1983). While Native American burning practices prior to the arrival of European settlers suppressed the encroachment of Douglas-fir and other woody vegetation, in Redwood Creek the loss of about one-quarter of the prairie and oak woodlands since 1850 is attributed to fire exclusion and road building (Popence et al. 1992).

Land Use

The Mattole Basin was occupied by Athabaskan-speaking Mattole and Sinkyone Native Americans when the first settlers from the Eastern United States arrived in the early 1850s. Disputes over hunting ground and domestic stock culminated in a massacre at Squaw Creek in 1864. Survivors were sent to the Round Valley Reservation on the Middle Fork of the Eel River, where most succumbed to the measles epidemic in 1868 (Elements of Recovery, 1989).

The first known white explorer of the Mattole Basin was John Hill of Fort Humboldt, who glowingly described, in an 1854 report, tall clover in the prairies, rich grassland in the valleys, and timbered slopes underlain by wild oats and other grasses (Humboldt Times Weekly, September 23, 1854). Within this report he noted streams with riparian corridors of alder, willow, and cottonwood and the Douglas fir and tan-oak on the slopes. He mistakenly described redwood forests in the nearby woods (W.W. Roscoe, 1940). He also commented on the numerous Indians who appeared to have not seen white men before.

In 1858, just four years after Hill explored the valley, and with the influx of new pioneers, farming began in earnest. The very first settlers were farmers and ranchers who converted native grassland into home sites, home gardens, orchards, and rangeland. As grazing activities increased, conversion of the adjoining forests began. Timber was harvested for local needs or simply felled and then areas broadcast burned for conversion to grazing lands. Just after the turn of the century, tannin produced from the bark of tan oak trees became a commercial commodity in the Mattole Basin.

In 1941, the most widespread use of the watershed appears to have been grazing and is indicated by the amount of grassland and recent fires, which appear to be deliberate conversion of pre-existing brush and timberland. Conifer timber harvesting activities are readily apparent near Harris Creek and continue further upstream into the redwood belt. Timber harvest operations began in earnest as Douglas fir became a merchantable building material during the post World War II boom.

The 1960s were the beginning of the back to land movement of young, largely urban people onto subdivided property, generally recently logged. Many of these new residents were interested in learning how to work on their land, to rehabilitate it, and to find an income.

By the late 1980s, timber harvesting decreased while environmental awareness increased. Changes in policy concerning management of federal lands and the designation of the Northern Spotted Owl as federally threatened led to the designation of BLM lands, a large proportion of the Western and a smaller percentage of the Eastern Subbasins, as Late Successional Reserve (BLM, Bear Creek 1995) lands that are not subject to harvest.

More recently, much of the land use in the Mattole Basin is centered on relatively small, private non-industrial timber management, cattle and sheep ranching activities, and other agricultural pursuits like orchards, pasture, and field crops.

Ranching has focused almost entirely on cattle since the passage of propositions limiting predator control options. County-wide, beef cattle numbers between 1980 and 2001 have ranged between 21,000 to 24,000 head, while sheep numbers have plummeted from 25,000 animals in 1980 to 15,600 animals in 1992 and 4,500 sheep in 1997, the latest figures available (http:/, 2002). Land holdings in the Mattole Basin are increasingly fragmented and the amount of livestock is difficult to quantify. Many of the smaller ownerships have hobby livestock, but there is no way to estimate numbers.

Current census data indicate that approximately 1200 people call the Mattole Basin their home.

Fish Habitat Relationships

Chinook Salmon

Mattole River Chinook salmon are fall-run, migrating into the river as adults from October through February and spawning during the same period. Shortly after fry emerge from redds, the gravel incubation nests built by spawning females, they begin to move downstream and arrive at the estuary throughout the spring. In California, most Chinook smolts enter the ocean during their first seven months of life. Chinook salmon generally mature at 3 to 4 years of age. Some precocious males mature at age two (commonly called jacks) and return to spawn and die along with the older, larger fish from earlier year classes.

In the Mattole River system Chinook salmon juveniles are detained in the estuary because of the creation of lagoon conditions early in the summer. This prevents them from going to the ocean until it reopens in the Fall. Unfortunately, conditions in the estuary through the summer are not hospitable and studies conducted by Humboldt State University within the past fifteen years have shown high, and perhaps total, mortality in some years. Juveniles that enter the ocean and survive to adulthood, usually return to the system after their third or fourth year at sea.

Coho Salmon

Coho salmon adults enter the Mattole River from October through December and reach the upper spawning reaches in November and January. In the shorter California coastal streams, most return from mid-November through mid-January. Spawning commences shortly after arriving at the spawning sites provided that water conditions, including flow and temperature are satisfactory.

Juvenile coho will normally attempt to remain in the stream, in the vicinity where hatched, for one year. However, environmental factors, such as low summer flows or high water temperatures, or population pressures due to limited rearing space and food, will force the smaller, weaker individuals to relocate. Most of this movement is manifested in a downstream migration of fry during the first spring and summer.

Steelhead Trout

Steelhead trout are an anadromous strain of rainbow trout that migrate to sea and later return to inland rivers as adults to spawn. In contrast to all Pacific salmon, not all steelhead die after spawning. In the Mattole River, upstream migration occurs from November through May with the peak run occurring in January-February. Mattole River steelhead spawners are typically age four or five years and weigh 2 to 12 pounds or more. Female steelhead carry an average of 3,500 eggs, with a range of 1,500-4,500.

In the Mattole River, steelhead generally migrate downstream as 2-year old smolts during spring and early summer months. Emigration appears to be more closely associated with size than age, 6-8 inches being the size of most downstream migrants.

Summer Steelhead Trout

Summer steelhead enter the Mattole River between March and June. Fish remain in clear, cool, deep pools until late winter and spring of the following year before spawning. Mattole River summer steelhead can be large in size, averaging 26 inches and 24 inches, or more for males and females respectively. Egg deposition occurs in early spring with the young hatching about 50 days later. Generally, young summer steelhead will remain in the Mattole River for two years followed by another one to three years of ocean life before returning to complete their life cycle. Ninety percent of the returning adults are three and four year old fish. (Adapted from Jones and Ekman, 1980.)

Fish Passage Barriers

Stream connectivity is essential for juvenile and adult anadromous fish. Stream connectivity describes the absence of barriers to the free instream movement of adult and juvenile salmonids. Free movement in well-connected streams allows salmonids to find food, escape from high water temperatures, escape from predation, and migrate to and from their stream of origin as juveniles and adults. Dry or intermittent channels can impede free passage for salmonids; temporary or permanent dams, poorly constructed road crossings, landslides, debris jams, or other natural and/or man-caused channel disturbances can also disrupt stream connectivity. Culverts are one potential fish passage barrier that has been examined in the Mattole Basin.

Culvert repair, upgrade, and improvement are an important part of stream restoration projects. In the Mattole Basin, the CDFG North Coast Watershed Improvement Program includes culverts as a part of stream restoration and improvement efforts and was able to supply NCWAP with information on recent culvert assessment and treatment contracts. Typically, following culvert assessments, the County or landowner follows up with improvement proposals to CDFG for funding support to implement recommendations. In the Mattole Basin, some of the recommended treatments are currently proposed or being implemented.

Fish History and Status

Fish species in the Mattole Basin
Fishery resources of the Mattole Basin include fall-run Chinook salmon, coho salmon, winter-run steelhead trout, and summer -run steelhead trout. Other fish present in the Mattole Basin include sticklebacks, lampreys, and sculpins. Two notable fish species that have apparently been extirpated in the Mattole Basin are spring-run Chinook salmon (CDFG 1972) and green sturgeon (Moyle et al. 1989).

Special Status Species
Ten plant and animal species in the Mattole Basin have been found to have declining populations across their ranges and thus warrant special concern. Species with declining populations are eligible to be listed under the federal Endangered Species Act (ESA) and the California Endangered Species Act (CESA) for special attention. Detailed explanations of federal and state listings criteria are in the CDFG Appendix F.

We have little specific information about the levels of abundance of mid-nineteenth century fishery stocks. However, based upon turn-of-the-century cannery records from the river systems in northwestern North America, including the neighboring Eel River, we can infer a great deal about the historic plenitude of Chinook, coho, and steelhead in the Mattole Basin. Old-timers and descendants of those early settlers, like Cecil Etter, born at the beginning of the twentieth century in a house that still stands near the confluence of Honeydew Creek and the Mattole River, reported an ever-ready supply of salmon and steelhead before the floods of 1955 and 1964. Those fish were easily caught for the table or smokehouse with a pitchfork or gaff hook in “any creek of the Mattole.” With a twinkle in his eye, he added, “before the war (WWII) no-one knew what a fishin’ pole was, or what one was good for in regards to salmon or steelhead,” (C. Etter, personal communication).

More recent accounts from Mattole anglers like Lynn Mantooth, “Hippie Bob,” and the “Nevada Boys,” fishing in the 1945 – 1970 period, describe a fabled sport fishery where in good stream conditions a group of four or five anglers could expect to hook and release over a hundred fish, mostly steelhead, in a day of fishing (J. Clary, personal communication). Salmon poaching beneath the Petrolia Bridge, and elsewhere, was a viable means of making a “little Christmas money” by selling fresh and smoked salmon as late as the 1960s, (C. Wright, personal communication).

By the late 1970s, those fish populations had collapsed to levels that alerted locals to their depressed condition, and initiated the formation of the Mattole Salmon Group. In 1981, the Mattole Salmon Group with the cooperation of landowners, and the support of the California Department of Fish and Game (CDFG), and others like the Mattole Restoration Council, began stock restoration activities that included public education, artificial propagation, and habitat improvements. Their efforts have been important in preserving the Mattole’s fragile fishery stocks in the face of very challenging conditions.

Special status species of the Mattole Basin
Fishing Interests, Constituents
Historically, during the winter months sport fishing for salmon and steelhead has drawn anglers from throughout California and other states to the Mattole River, which has been an important contributor to both sport and commercial marine fisheries. Due to declining populations, Chinook and coho salmon, and steelhead are currently listed as threatened under the federal Endangered Species Act. The threatened status now restricts river sport fishing on Mattole Basin stocks. The Mattole Estuary, from the river mouth to 200 yards upstream, is closed to fishing all year. The winter salmon and steelhead fishery of the Mattole River is managed as a catch and release fishery from January 1 to March 31. (Always consult CDFG fishing regulations for dates and other information.)

Fish Restoration Programs
Local watershed groups, the BLM, various state agencies such as CDFG, and local landowners have worked on numerous restoration projects throughout the Mattole Basin. The Mattole Restoration Council (MRC) and the Mattole Salmon Group (MSG) have obtained contracts for work on such diverse areas of restoration as stream surveys, road assessment, revegetation, instream habitat improvement, fish rearing, public education, and monitoring.