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[lJ13]8 B. Geologic and Hydrologic Setting of the Claim Sites and Study Sites Most of the claim and study watersheds are in the Northem Rocky Mountain Physiographic province (F enneman, 1931). The exception is Rapid River which is in the Columbia Intermontane Province. All claim sites are within the Snake River Basin. as are all fluvial process study sites, with the exception of Catspur Creek in northern Idaho. Elevations at the stream gage locations range from 1,453 to 6,390 feet above sea level (Table 2). Typically these streams and rivers reach peak flows in April, Mayor June in association with spring snowmelt. High flows occasionally occur in fall and winter in association with cyclonic storms and with rain-on-snow events. Rain-on-snow events are more common at lower elevations. Even those watersheds with relatively low gage elevations: Selway River, Lochsa River, North Fork Clearwater River, Canyon Creek, Fish Creek, and Rapid River, have most of their drainage area at higher elevations and snowmelt is the dominant annual hydrologic event. Kjelstrom and Moffat (1981) found an increasing percentage of the highest streamflow peaks are associated with rainstorms with an increasing percentage of the drainage area below 6,000 feet. They suggest that drainages with less than 20 percent of their area below 6,000 feet be considered dominated by snowmelt generated peaks, and drainages with a mean basin elevation of less than 3,000 feet be considered dominated by rainstorm peaks. For those basins falling between these two situations, peaks could be generated by either rainstorms or snowmelt. Generally, streamflows drop rapidly over the summer with the disappearance of the snowpack, but on occasion increase due to thunderstorms. Low flows are reached in September or October and remain relatively low during winter months. Frontal systems moving eastward from the Pacific Ocean are the source of most precipitation. As these systems are lifted over the mountains, they cool and release their moisture. Thus, it is common to see increasing precipitation with increasing elevation throughout the State. Average annual precipitation in these basins ranges from about 10 inches to over 70 inches (University of Idaho, 1995). In most areas, winters are wet and summers are relatively dry. At higher elevations snow accumulates from fall through spring. Accumulated spring snowpack may account for over half the annual precipitation. Rainstorm activity in the summer months is generally in the form of thunderstorms associated with unstable air masses. Rainfall is generally of a shon duration but may be of high intensity. There are a variety of rock types in the watersheds encompassing the channel maintenance claim sites and the fluvial process study sites (Table 2). One of most notable geologic features is the Idaho batholith, a large igneous intrusion in central Idaho that extends about 250 miles in a north-south direction and 90 miles in an east-west direction (Bennett, 1974). Nine of the channel maintenance sites and eleven of the fluvial process study watersheds have a large ponion of their area on the batholith. Many areas of the batholith are characterized by rock that weathers deeply to produce coarse sandy soils with high erosion rates if disturbed. Other lithologies at these sites include metamorphic material usually associated with the border of the batholith, mixed volcanics in watersheds in the upper portion of the Salmon River basin, and sedimentary rocks associated with the Seven Devils formations, or the upper portion of the Salmon River basin, or the vicinity of the Lemhi River basin. United Slates' Expert Report Disclosing _Iogies for Quantilication of Organic Ad Claims CcInsoIidated Subcase No, 63-25243 18