San Mateo Creek's source elevation is at almost 1,000 feet on Sweeney Ridge from which it flows southeasterly (in a valley east of Cahill Ridge and west of Sawyer Ridge) for 11.2 km (7 mi) before entering the northwest arm of Lower Crystal Springs Reservoir.
From the Crystal Springs Dam San Mateo Creek flows generally northeast 8 km (5 mi) through San Mateo where it is partly intermittent and altered, to San Francisco Bay about 1.1 km (0.7 mi) west of the mouth of Seal Slough [REF].