Though it begins as a wild stream in the Mayacamas Mountains, Santa Rosa Creek is culverted for part of its course through the city of Santa Rosa's downtown. The riparian area has a rich prehistoric past with settlement of the Southern Pomo people on much of the middle and lower reach banks. A significant stream restoration project was created in the downtown Santa Rosa reach in the late 1990s, allowing steelhead and coho salmon to migrate to productive upstream spawning areas. Major tributaries to Santa Rosa Creek include Brush Creek, Piner Creek, Matanzas Creek and Colgan Creek. Annual precipitation in the Sonoma Creek watershed is about 24 to 38 inches (60 to 70 centimeters). Water quality sampling in the Railroad Square area of Santa Rosa indicate coliform bacteria standards are often exceeded.