Landscape Photo

Arroyo Aguague Map


Total Acres: 874
Total Expenditures: $6,594,000


Acquisition History      
xxxxDate   Property
  Preservation Type xGrants & Partners
  Fee Purchase  
  Easement Purchase  
  Fee Purchase  
  Fee Purchase xCoastal Conservancy,
              xxx$100,000; Bay Area
              xxxRidge Trail, $150,000

* As approved by board resolution      



Situated on the westernmost slopes of the Diablo Range, the Arroyo Aguague study area is bordered on the east by The Nature Conservancy’s protected lands and on the west by the Santa Clara Valley floor. Alum Rock Park forms the area’s northern border.

The study area is named for the tributary to Upper Penitencia Creek that flows through its steep canyons. The stream has its headwaters in Joseph D. Grant County Park, which forms the southeastern border of the area.

General Features

California annual grasslands and coast live oak-blue oak woodland compose the dominant plant communities in the foothills of Arroyo Aguague. Cattle grazing was historically important in the region and continues today.

The southern reaches of Penitencia Creek and Arroyo Aguague drain this portion of the Diablo Range. These tributaries are critical waterways for steelhead trout. Many springs and small creeks also provide potential riparian habitat for California red-legged frog (Rana aurora draytonii) and other amphibians.

Arroyo Aguague photo
Arroyo Aguague
Arroyo Aguague is located between the Hayward and Calaveras faults. Geologists have recently concluded that the two faults are connected far below the earth’s surface. This raises the possibility that a future earthquake might rupture on both faults simultaneously, creating a tremor far stronger than the historic 1868 Hayward quake.

The steep hillsides and deep canyons offer outstanding scenery as well as views of the valley floor from the highest knolls. Recognized for its outstanding value, the lands along Penitencia Creek were protected by the City of San Jose as Alum Rock Park in 1872, the first municipal park in the United States.

Other protected lands in the Arroyo Aguague study area are the 874 acres preserved by the Open Space Authority.

Authority Lands

The potential for extending an important regional trail network brought three partners together in 2003 to make the first purchase in this area. The Authority, with contributions from the Coastal Conservancy and Bay Area Ridge Trail, purchased 67 acres with ridge top views and access to Mt. Hamilton Road.

shell-encrusted rock photo
Shell-encrusted rock

A second purchase in the same year added a 520-acre parcel of native grasslands, mixed chaparral and coast live oak-blue oak woodland. An unnamed creek running through the center of the property provides outstanding riparian habitat. Toads and tree frogs have been seen in the wetlands and the potential for sheltering California red-legged frogs is strong.

A trail easement acquired in 2005 connected lands in this study area and OSA properties north of Alum Rock Park. With the purchase of the 233-acre Moore Property in 2006, a key stretch of creek and hillsides visible from the park was protected forever.