Marble Fork of the Kaweah River

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The headwaters of the Marble Fork of the Kaweah River (36°36'22"N, 118°40'59"W) are located in the Tokopah Valley of Sequoia National Park. The Tokopah Valley includes Emerald, Pear and Topaz lakes which, along with several other small ponds and lakes, comprise approximately 30 ha of the basin's 1,908 ha drainage area. The river is a second order stream at the gauge near the mouth of the valley (elevation 2,621 m). The highest point in the watershed lies at an altitude of 3,493 meters. The V/A index for the Marble Fork watershed is small, suggesting that lakes and ponds in the basin have little influence on river discharge or chemistry. The river never went dry at the gauging station, but during droughts most of the river, except for a short stretch immediately upstream of the gauge, goes dry early in the autumn.

The geology of the Tokopah Valley is dominated by fine and medium-grained, porphyritic granodiorite and coarse-grained granite. Most of the basin is composed of bedrock and talus but there are significant areas of Wet Meadow Soils in upper portions of the basin (i.e., Table Meadows) and on the margins of the river. Trees, mainly Lodgepole Pine, Western White Pine and willows, are found along the river as it meanders through the valley. The higher elevations of the catchment, including the upper portions of the Pear and Emerald lake watersheds, have little vegetation, mostly sedges and grasses.

Brook trout have been observed in the river but appear to be restricted to reaches below the confluence of the Pear Lake outlet. Just above this confluence is a steep gradient of smooth bedrock. Flows are rapid and turbulent during snowmelt and under low-flow conditions the river fans out over the rock surface, reducing water depths to just a few centimeters. These conditions preclude the migration of trout upstream and may partially explain the absence of fish in the upper reaches of the river and at Topaz and Frog lakes.