Forty minutes from Sunnyvale is the Sunol Wilderness. The Sunol Wilderness is one in a chain of regional widerness parks in southern Alameda County. This remote and beautiful land is the domain of abundant wildlife, including eagels, red-tailed hawks, turkey vultures, deer, coyote, bobcats, and mountain lions.
The land is studded with oak and bay, carpeted with springtime wildflowers, and manteled briefly in white after winter storms.
A popular and easy hike is the Little Yosemite Trail. Alameda Creek has its headwaters further south in the shadow of Mt Diablo and passes through this wilderness on its 28-mile route to San Francisco Bay. A section passes through a ravine and is known as Little Yosemite. The trial is rated as easy: A mile or so out and then back; not much elevation.
Further along is a side trail called W Tree Rock Scramble.
If you are going on the trails other than Little Yosemite, then read on:
Before starting your trip from Sunol headquarters to the backpack area, be sure to obtain an ample supply of water; there is no drinkable water along the way.
A variety of trails lead to the backpack area, but the main route crosses Alameda Creek, then follows Canyon View and McCorkle trails up a steep grade to the intersection with the Cerro Este fire road. The trip from this intersection to the backpack area is a narrow, downhill path 1.2 miles long. Note the stone cairns directing the way.
The elevation changes from the park headquarters to the Cerro Este intersection is 1,040 feet in 2.09 miles. Then there is a 280-foot descent in 1.28 miles to the backpack area. Water faucets at the backpack area are your last chance to obtain drinkable water until you reach the next campsite (Doe Canyon Horse Camp, about 5 miles and 2500 feet higher up).
The Ohlone Trail has little shade is is strongly discouraged for summer hikes. There is no potable water so bring liters of your own. And by not-potable, I mean that the clear-flowing stream you see has hundreds of cow patties a hundred yards upstream (Grazing cows are still allowed).