YOSEMITE Vegetational Changes in Yosemite Valley NPS Occasional Paper No. 5

The Merced River, which flows through Yosemite Valley, drains westward from the central Sierra Nevada in California at approximately latitude 37°45' N. and longitude 119°35' W. A Mediterranean-type climate prevails with cool wet winters and hot dry summers. Monthly mean temperature ranges from 1.33°C in January to 21.56°C in July. The mean annual precipitation for a 56-year period was 950 mm (38 inches) of which 30 mm (1.2 inches) fell from June through September. Snow falls every winter but it usually melts rapidly (U. S. Weather Bureau 1961). Elevations above sea level are 1,250 m (4,125 feet) at the upper end of the valley and 1,180 m (3,894 feet) at the lower. The valley is about 11 km (6.6 miles) long and 0.8 km (0.5 miles) wide. The 1,220 m (4,000 feet) contour on the 1961 U. S. Geological Survey map coincides approximately with the foot of the talus slopes and contains over 890 ha in its loop around the valley above Pohono Bridge.