GEOLOGY AND TOPOGRAPHY

construction and timber harvesting have occurred. Soils developed from serpentine are usually unproductive due to high amounts of magnesium.

The Western Cascades Province topography is also deeply dissected but tends to be less rugged, with rounded mountain peaks. Bedrock material is typically volcanic: andesite, basalt, and tuffs and breccias. Mass movement is a dominant erosion process in this province and results in terrain marked by basins below steep headwalls and massive rock bluffs.

The High Cascades Province consists of a narrow, gently sloping plateau of basalt and andesite capped with a chain of young volcanic peaks (USDI GS 1969). Pockets of pumice and ash, recent lava flows, and glacial deposits are scattered over the plateau. Topography is rolling, with average relief of 1,600 feet. Soils developed from pumice and ash are unstable, particularly on steeper slopes.

2.4 SOILS

The "Soil Inventory of the Medford District" (DeMoulin et al. 1975) describes in detail the soils of the JKS YUS at the series level. Maps of the soil series associations are contained in the inventory, which may be examined at the Medford District Office or the Oregon State Office of BLM. A summary of the soil mapping units, their properties, and the acreages as described in the inventory, appears as Appendix F.

The Medford District developed a general soils map by combining soil associations that have similar properties (Figure 2-4).

The rate of erosion in the JKS YUS has been inferred from the following studies (Table 2-2) on other timberland in the Pacific Northwest because no studies are available in southwestern Oregon. Based on these studies and the weighted average of geologic formations in the JKS YUS, the overall erosion rate of undisturbed lands is estimated to be 35 tons per square mile per year.

Three types of rock found in the JKSYUS (granite, serpentine, and tuffs and breccias) have weathered to soils which have caused problems in the timber management program. Soils formed from granitic rocks have high sand and low clay content and are highly erodable and very unstable on steep slopes. These soils include the Siskiyou (721), Holland (722), and Rogue (861) soils and are located predominantly in the Evans Creek drainage of the Klamath Mountains Province. Soils formed on serpentine have high clay content, shallow profiles, and restricted vegetation due to magnesium toxicity. Droughtiness, due to shallow profiles and high clay content, together with the magnesium toxicity severely limits timber production on serpentine soils. Small areas of the Pearsoll soil (770) are found along the western margin of the JKS YUs. The TPCC process has eliminated most of the serpentine soils from the high intensity lands of the JKS YUs (see Section 1.2.1). Soils formed from weathered

tuffs and breccias which include Carney (704), 705, Medco (706), Laurelhurst (745), 840, 842, and 850 soils, are often unstable and very easily eroded. Road construction through tuffs and breccias increases the incidence of mass movement (i.e., slumps).

2.5 WATER RESOURCES

All of the Jackson and Klamath SYUS lie within either the Rogue River Watershed (80 percent) or the Klamath River Watershed (20 percent). Essentially, the Klamath SYU drains into the Klamath River and the Jackson SYU into the Rogue River system.

Within the JKS YUS, there are approximately 765 miles of Class I streams (see Glossary). Approximately 195 miles of these are on public lands.

Reservoirs within the planning area (Appendix G) have an effect on water quality and on availability of water for hydroelectric power production, irrigation, and commercial and domestic uses. Most were built primarily for irrigation purposes but have other benefits and uses, such as flood control, water quality enhancement, and recreation. Howard Prairie, Hyatt Lake, Little Hyatt Lake, Keene Creek (all in the Klamath River drainage), and Emigrant Creek Reservoirs are all interconnected by a series of canals, siphons, and one small hydroelectric plant, and discharge into the Rogue River drainage.

Water movement in the forest is an important element in watershed relationships. Definitions of terms used to describe water movement may be helpful at this point. Runoff is that part of precipitation, as well as any other flow contributions, which appears in surface streams, either perennial or intermittent (Chow 1964). There are three basic components of runoff: overland flow, subsurface flow, and groundwater flow. Overland flow moves over the land surface to stream channels, subsurface flow moves laterally through the upper soil horizons toward streams, and groundwater flow moves from deep water saturated zones to streams.

Subsurface flow accounts for nearly all runoff in western Oregon forests (Harr 1976). Water not stored in the soil profile, the underlying rock, or taken up by plants either moves by subsurface flow to stream channels or percolates to groundwater.

Soils in the Jackson SYU are normally less than 40 inches deep and are underlain by rock of low porosity. Together the soil and bedrock can store only a fraction of the total precipitation, so excess water moves readily to stream channels and the resulting streamflow rises and falls with changes in seasonal rainfall. Underlying basalt in the Klamath SYU, however, is much more porous and stores water, making groundwater rather than subsurface flow the main component of streamflow in this area (Pacific Northwest River Basins

FIRE

Commission 1970, pp. 856-8). Variations in streamflow in the Klamath SYU, therefore, would not be so closely linked to precipitation patterns.

Appendix G contains annual and monthly water yield data of major streams in the JKS YUS.

2.5.2 Water Quality

Present water quality generally meets with water quality standards established by Oregon Department of Environmental Quality (ODEQ) to fulfill their "nondegradation" policy (ODEQ 1976 c,d). Appendix G contains water quality descriptions and a summary of water quality at various sampling sites on the Rogue, Klamath, and Applegate Rivers and at selected reservoirs.

Present non-point source pollution problems in the JKS YUS include those of elevated water temperatures, nuisance algae and aquatic plant growth, excessive debris, sedimentation, streambank erosion, and water withdrawals causing stream-quality problems (ODEQ 1978). A composite map of these problems was made and showed that Evans Creek, South Fork Little Butte Creek, the Applegate River, and Bear Creek had major non-point source pollution problems. The nature of these problems is shown in Table 2-3.

2.6 FIRE

In the 12 years from 1966 to 1977, the number of fires occurring annually on BLM-administered lands in the JKS YUS has ranged from 15 to 39, with an average of 30 fires per year. Acreage burned annually varied from 5 to 976 acres, with an average of 231 acres. Although 69 percent of the fires were caused by lightning, fires caused by people accounted for 96 percent of the acres burned (BLM Fire Report Files, OSO).

The fire season in the SYUS generally begins in May and often lasts until mid-October. The high temperatures, low humidity, and low humidity, and numerous isolated thunderstorms common this time of year are conducive to forest fires. It is also the major recreation season.

Vegetation within the JKS YUS combines elements of the California, north coast, and eastern Oregon floras. The planning area contains specimens of many plants which are growing on the edge of their natural range or are unique to the region. The eastern Siskiyou Mountains are especially rich in endemic and relict species (Waring 1969).

For purposes of this ES, vegetation is generally described in terms of "zones" adapted from those identified by Franklin and Dyrness in their Natural Vegetation of Oregon and Washington (1973). Unless otherwise noted, all vegetation