San Justo Dam


San Justo Dam and Reservoir

San Justo Dam and Reservoir are located near the center of the Coast Ranges Province of California.  The province is characterized by north-west-tending valleys and mountain ranges formed along major faults as a result of plate tectonic stresses.   The mountain ranges consist of uplifted, pre-Cenozoic "basement" rock, comprising a series of narrow v-shaped canyons and ridges flanked by rolling foothills. 

The Diablo Range to the east is underlain by two different rock units, the Franciscan Assemblage and the Great valley Sequence.  To the west, the Gabilan Range is underlain by the granitic Sur Series where "basement" rock is partially blanketed by Cenozoic sedimentary rock. 

East and south of Hollister, the Diablo Range and the Gabilan Range are capped by Mesozoic volanic flows.  The valleys are filled with Cenozoic marine and nonmarine sediments.  In the valleys east of the San Andreas Rift Zone, Pliocene lakebed sediments are common below elevation 122 meters.

The reservoir and damsite are located wirthin the eastern foothills of the Gabilan Range.  In this area, the foothills are underlain by unindurated, compact sediments believed to be of Pliocene-Pleistocene age.

RegionFacilities in Mid-Pacific | Mid-Pacific Home Page
CountySan Benito
ProjectCVP-San Felipe Division
Dam Type
ReservoirSan Justo
WatercourseOfftream Storage
Original Construction1987
Modified Construction
National ID NumberCA82934
Hydrologic Unit Code

Structural Height135.0 ft
Hydraulic Height (Normal Operating Depth at Dam)126.0 ft
Top Parapet (Elevation)
Spillway Crest Elevation504.1 ft
Crest Elevation508.5 ft
Crest Length1115.0 ft
Crest Width
Base Width
Volume of Dam Construction Materials
Streambed at Dam Axis370.7 ft
Top of Exclusive Flood Control Pool (Elevation)
Top of Joint Use Pool (Elevation)503.3 ft
Top of Active Conservation Pool (Elevation)500.0 ft
Top of Inactive Conservation Pool (Elevation)419.9 ft
Top of Dead Storage Pool (Elevation)410.1 ft

Hydraulics & Hydrology
Total Water Storage at Elevation
Maximum Water Surface Elevation
Normal Water Surface Elevation503.3 ft
Spillway Type
Auxiliary SpillwayNo
Spillway Capacity at Elevation0 cfs at 504.1 ft
Auxiliary Spillway Capacity at Elevation
Uncontrolled Spillway Capacity at Elevation
Outlet Works Capacity at Elevation98.8 cfs at 503.3 ft
Diversion Capacity at Elevation
Drainage Area0.74 sq mi
Hydrometeorological Report (HMR)HMR 36
Probable Maximum Flood (PMF) Report

Contact Information
TitleArea Office Manager
OrganizationSouth-Central California Area Office
Address1243 "N" Street
CityFresno, CA 93721-1813
Phone (Office)559-487-5116
OrganizationSan Benito County Water District
AddressPO Box 899
CityHollister, CA 95024-0899
Phone (Fax)831 637-7267
Phone (Office)831 637-8218

Last updated: Jun 04, 2009