Located in the Diablo Range backcountry east of Morgan Hill, CA - between the San Antonio Valley (north) and
Pacheco Pass (south), the park consists of a series of high ridges separated by steep walled canyons, with occasional level valley bottoms and distinct peaks. Most of the ridges run around in elevation, with canyon bottoms usually around above sea level. The highest point in the park is on the northernmost boundary, at about elevation. This point may be considered to be on the slopes of
Mt. Stakes, a mile north of the park's northern boundary. (Mt. Stakes, at , is the highest point in Stanislaus County). The lowest point in the park is at the
Bell Station access point in the southeast; this is only a little above in elevation. Since this is a mere strip of land along a road right-of-way, it is often not thought of as an integral part of the state park. The lowest point in the main body of the park is the place where the North Fork of
Pacheco Creek flows out, at about elevation, also in the southeast corner. Prominent ridges and peaks in the park, from west to east and north to south, include Pine Ridge, Middle Ridge, Blue Ridge (with
Mount Sizer the highest point), Rock House Ridge,
Bear Mountain, Bear Mountain Peak,
Robison Mountain (not Robinson Mountain as it is too often misspelled),
Rooster Comb, Palassou Ridge, Mahoney Ridge (and Mahoney Meadows), Willow Ridge, Pacheco Ridge,
Mustang Peak, Walsh Peak, Willson Field Hill, Wasno Ridge,
Burra Burra Peak, Willson Peak, Rock Springs Peak, and Phegley Ridge. The park is divided into 13 zones on the official map. From West to East, and North to South, they are: • Western Zone (Park HQ) • Blue Ridge Zone (Mt Sizer, Hat Rock) • Interior Zone (Bear Mountain) • Mississippi Zone • Orestimba Wilderness Zone • Mustang Peak Zone • Mahoney Zone • Coit Zone • Pacheco Zone (Dowdy Ranch Entrance) • Grizzly Gulch Zone • Kelly Zone • Dormida Zone • Phegley Zone (Bill's Hill, Redfern Pond) The park map also shows 1) Thomas Addition (near Mt. Sizer) and 2) Lakeview Addition (just below the park's HQ) to which there is no public access as of now (late 2013), nor any plans yet to make those areas accessible to public. The area encompasses parts of three major watersheds:
Coyote Creek,
Orestimba Creek, and
Pacheco Creek. Coyote Creek is fed by Grizzly Creek, the Little, Middle, and East Forks of Coyote Creek, Kelly Cabin Canyon, Grizzly Gulch (not be confused with Grizzly Creek), and Hunting Hollow. Coyote Creek flows into Coyote Lake and Anderson Lake, and then north through San Jose into the San Francisco Bay. The
South Fork Orestimba Creek originates in the park, and is fed by Red Creek, Pinto and Robinson creeks, and Lion Canyon. After joining the North Fork outside the park, it flows out to the
San Joaquin Valley, where it joins the
San Joaquin River. The latter runs more or less north and, if it were not diverted, would flow out to
San Pablo Bay. The
North Fork Pacheco Creek also originates within the park, and it is fed by
Mississippi Creek.
Cañada de la Dormida independently reaches Pacheco Creek outside of the park boundaries. If not diverted, the waters of Pacheco Creek would eventually reach
Monterey Bay via the
Pajaro River. There is a fourth, minor watershed within the park: the small creeks of the
Upper San Antonio Valley in the north flow into
San Antonio Creek north of the park. This, in turn, joins
Arroyo Valle, which flows into
Alameda Creek, then flows into
San Francisco Bay west of the city of
Fremont. The creeks are all seasonal; none of them flow year-round, though all have holes in which water may be found during all seasons. Depending on rainfall and temperatures, the creeks generally flow from November to May. After heavy rainfall, the creeks can become impassable, raging torrents, though usually they are not difficult to ford if one does not mind getting wet or (in winter and early spring) cold. The park contains dozens of reservoirs created by the former ranch owners for watering cattle and for recreational fishing and hunting. The largest is Mississippi Lake, at about and long. Other notables are Coit, Kelly, Jackrabbit, and Paradise lakes. ==Ecology==