 Historical records indicate that Chinook salmon ("Oncorhynchus tshawytscha") occurred in at least two San Francisco Bay Area watersheds, San Mateo Creek in San Mateo County and San Leandro Creek in Alameda County.Fog drip may play a key role in the precipitation in the upper watershed.On Cahill Ridge, just west of San Mateo Creek and east of Pilarcitos Creek, at an altitude of 1,000 feet, Oberlander measured fog drip beneath tanoak ("Lithocarpus densiflorus"), coast redwood and three Douglas fir trees, the latter 125 feet tall.