The section of the Arroyo las Positas extends 300 feet upstream from the North Livermore Avenue Bridge across the Arroyo las Positas. This is the site of the historic USGS stream flow monitoring station. The property is owned by Caltrans. A trail is planned along the south side of this arroyo but currently there is no trail. The year-round stream flow originates from rising groundwater in the Springtown area. The watershed extends from Tesla Pass to Brushy Peak and includes the Labs and all of Springtown. The Arroyo las Positas conveyed the first historic State Water Project flows in May 1962 when water from the South Bay Aqueduct was released into Altamont Creek and flowed down the Positas for local groundwater recharge and for recharge in the groundwater basins in Freemont. The waters in the Positas have higher mineral content. There is no suitable habitat within the Positas watershed for steelhead or other cold water fish and the Positas is not considered a migratory route for fish.
Trash in the arroyo comes from occasional homeless camps, from windblown trash and from urban storm drain runoff upstream of this site.