Off Vasco Road between Brentwood and Livermore, sandstone outcrops rise from the hills. Visitors can only see them on a guided tour.
Why it's closed
The park district says the preserve exists through the combined efforts of the district and the Contra Costa Water District, which jointly acquired it. All access is by advance-reservation guided tour, to protect its fragile resources. Tours run on select dates in fall, winter and spring, and visitors ride district buses from Round Valley Regional Preserve in Brentwood or Brushy Peak Regional Preserve in Livermore. There is a fee, dogs are not allowed, and reservations are on the district's registration page under the keyword "Vasco."
What's there
Wikipedia says the preserve protects wildlife habitat, chaparral and woodlands, native plants and Native American rock art. Vernal pools on top of the rocks are home to fairy shrimp, and nearby springs harbor red-legged frogs. Kit foxes, coyotes, eagles and hawks are often seen. The area is thought to have been a ceremonial site, and the rock art includes images of birds, along with deeply carved bedrock mortar holes used for preparing food. The first land was acquired in 1989, and in December 2009 the two agencies agreed to buy 1,644 adjacent acres. That tract, which has wind turbines, is held as a land bank and isn't open to the public.