Almaden dam and reservoir is one of the six original reservoirs in the county. Built across the Alamitos Creek, approximately 12 miles south of downtown San Jose, it was completed in 1935. The zoned earthfill dam has a height of 110 feet (downstream toe to crest) and a crest length of approximately 500 feet. The reservoir can store 1,586 acre-feet of water. Its surface area is 57 acres.
"Almaden" in Spanish means "mineral" or "mine." In 1845, Andres Castillero discovered a quicksilver (mercury) deposit in the area now known as the Almaden hills. At one time, the New Almaden Mine was the largest mercury-producing mine in the Americas. The dam and reservoir are located in these same hills.