Arroyo Mocho is a 34.7mi stream which originates in the far northeastern corner of Santa Clara County and flows northwesterly into eastern Alameda County, California. After traversing the cities of Livermore and Pleasanton it joins South San Ramon Creek to become Arroyo de la Laguna, which in turn flows to Alameda Creek and thence to San Francisco Bay.HistoryArroyo Mocho means "cutoff creek" because it historically had no outlet but dissipated into the ground after spreading out into many smaller streams between Livermore and Pleasanton. As early as 1852 it was also called Mocho Creek.Watershed and CourseArroyo Mocho originates on the western slope of 3684ft Mount Mocho in the northeast corner of Santa Clara County and flows west to Mines Road which it follows northwest into Alameda County. It passes Sweet Springs, a magnesia spring known for its sweet taste. Although historically it sank into the area between Livermore and Pleasanton now the site of multiple gravel pits, there is an engineered channel connecting it to Arroyo de la Laguna.The underlying aquifer is the Mocho Subbasin, whose eastern boundary is the Tesla Fault. Some groundwater flow occurs across this fault boundary, but flows are discontinuous below a depth of across the Tesla Fault and south of the Arroyo Mocho channel across the Livermore Fault.
