Arroyo del Valle or Arroyo Valle[1] is a 36.4-mile-long (58.6 km)[2] westward-flowing stream in Alameda County and Santa Clara County, California, USA, that is tributary to Arroyo de la Laguna which in turn flows into Alameda Creek. The stream drains much of the southern portion of the city of Livermore, and it also flows through and drains a considerable fraction of the city of Pleasanton. Water quality measurements in this stream indicate a pH level of 7.0, or neutral with respect to acidity; phosphate levels were not detectable.[3] In previous times the Arroyo del Valle had a significant steelhead migration; however, degradation of the stream in the latter half of the 20th century has decimated this anadromous fish population. [4]
In the middle reaches of Arroyo del Valle south of Livermore, there has been considerable historic grazing use. Depth to groundwater in this reach of the watershed typically ranges from 50 feet (15 m) to 100 feet (30 m) and flows to the west.[5] Subsequent to this reach, the Arroyo del Valle flows down the moderately sloping hills to enter gravel pits, where extraction (but not processing) has historically been conducted by Lone Star Industries.
Coordinates: 37°39′43″N 121°54′22″W / 37.6618757°N 121.9060688°W
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