The pyramid-shaped island tufa that lies along the east shore of the lake and is the reason the lake was named Pyramid Lake. Pyramid Lake is the geographic sink of the Truckee River Basin, 40 mi (64 km) northeast of Reno. Pyramid Lake is fed by the Truckee River, which is mostly the outflow from Lake Tahoe. The Truckee River enters Pyramid Lake at its southern end. Pyramid Lake has no outlet, with water leaving only by evaporation, or sub-surface seepage (an endorheic lake). The lake has about 10% of the area of the Great Salt Lake, but it has about 25% more volume. The salinity is approximately 1/6 that of sea water. Although clear Lake Tahoe forms the headwaters that drain to Pyramid Lake, the Truckee River delivers more turbid waters to Pyramid Lake after traversing the steep Sierra terrain and collecting moderately high silt-loaded surface runoff. Pyramid Lake is the site of some of the Earth's most spectacular tufa deposits. Tufa is a rock composed of calcium carbonate (CaCO3) that forms at the mouth of a spring, from lake water, or from a mixture of spring and lake water. The explorer John C. Fremont (1845) wrote about the tufas during his 1843-44 expedition and named the lake after the pyramidal-shaped island that lies along the east shore of the lake. The Paiute name for the island is Wono, meaning cone-shaped basket. The Paiute name for the lake is Cui-Ui Panunadu, meaning fish in standing water.