Alum Rock Park: Wikis


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Termite-eaten trail sign

Alum Rock Park, founded in 1872, was the first municipal park in the U.S. state of California. Located in a canyon in the Diablo Range foothills on the east side of San Jose, the 720 acre (2.9 km²) park offers 13 miles (21 km) of trails, varying from fairly level along Penitencia Creek to sharp switchbacks climbing to the ridges to the South Rim Trail and the North Rim Trail. The narrow floor of the canyon includes a visitor center, picnic areas, a playground, and sand volleyball pits.

The ridge trails offer superb views of Santa Clara Valley and of the canyon in which the park is located. Trails in the park also connect to the Bay Area Ridge Trail and the Boccardo Trail, which leads into part of the Santa Clara County Open Space Authority's property.

Equestrians and mountain bikers have access to some of the park's trails, while others are reserved for hikers only. High school cross-country meets from schools around the area are held at the park often.

View of northern Silicon Valley from South Rim Trail



Black-tailed deer in Alum Rock Park.

The steep sides of the canyon demonstrate the diversity of vegetation native to California. The south-facing slopes primarily consist of grasses, Poison Oak, sagebrush, and occasional live oak trees. The warm sun on the sagebrush lends a sweet smell to the air not found in the suburban Santa Clara Valley.

The north-facing slopes are dominated by trees, including Coast live oak, California bay laurel, madrone, and California buckeye. On the canyon floor, in the moist areas along Penitencia Creek, bigleaf maple, white alder, and Western sycamore provide ample shade for the abundant ferns.

Several larger varieties of birds frequent the park, including the Red-tailed Hawk, Turkey Vulture, Wild Turkeys, Great Egrets, and California Quail. Larger wildlife includes Black-tailed Deer, bobcats, and an occasional mountain lion. There has been an increase in the Mountain lion population in the San Francisco Bay Area and one should know how to respond to these animals if encountered. Please see the mountain lion safety tips in the Mountain Lion article.

When hiking, be careful to stay on the trail. Rattlesnakes (specifically, the Northern Pacific Rattlesnake: Crotalus oreganus) are known to be active during the summer months. They can occasionally be seen shading themselves in the foliage along the trails.

Youth Science Institute - Alum Rock Science and Nature Center

Opened in 1953, the Youth Science Institute - Alum Rock Science and Nature Center, operated by the Youth Science Institute, features natural history exhibits and a collection of live teaching animals, including several injured and non-releasable hawks and owls that are found in the region. The center offers nature and science school and group programs, after-school science and summer camp programs.


One of several bridges over Penitencia Creek

Alum Rock Park was originally known simply as "the reservation"; it received its current name around the turn of the 20th century when people mistook the white powdery appearance of a large rock near its entrance to mean that it contained alum.[1]

The canyon has abundant mineral springs, which were touted as beneficial to people's health. In the late 1800s and through the 1930s, the park was famed throughout the country as a health resort. Through those years and as late as the 1970s, the park featured a natatorium (a huge, heated indoor swimming pool), dozens of private heated mineral baths that visitors could rent, a restaurant, and various other buildings. Many of the springs were enclosed in stonework grottos, and stone bridges were built across the creek. An electric railroad brought people from San Jose into the park.

Grotto stonework around one of many mineral springs

From 1921 until unknown, the Santa Clara County Council of the Boy Scouts of America was given exclusive access to 15 acres (61,000 m²) in the park. By the 1960s, the park attracted so many visitors from the rapidly growing Santa Clara Valley that its facilities became overburdened and the natural scenery was damaged. In the 1970s, the park removed most of the buildings, closed off parts of the park, and began emphasizing the park's natural attractions rather than its man-made ones. Much of the attractive stonework remains, however, as do old support structures for the railroad.

Due to overuse, some of the springs became extinct, and surviving ones became very weak, producing very little output.

Penitencia Creek had a different name until the early 1900s; somehow it began to be called by the name of a different creek located to the north of Alum Rock Canyon, which was so-named because monks (possibly from Mission San Jose) would meditate by its waters.

El Niño winter storms caused a landslide that resulted in the closure of the original Alum Rock Avenue entrance in the autumn of 2000; access is currently available only from Penitencia Creek Road.

On October 30, 2007, the 2007 Alum Rock earthquake, a 5.6 earthquake hit the Bay Area at 8:04 pm Pacific time. It was centered 5 miles (8.0 km) NNE of Alum Rock and at a depth of 5.7 miles (9.2 km). The Hayward Fault and Calaveras Fault converge close to Alum Rock Park. One effect of the earthquake was to cause a previously dried spring to begin flowing again.

Private residents

There are also private residents who have access to the road that enters the park, and continues on to the rear parking lot. At the end of the parking lot is a metal gate which requires a security code number to enter. You can walk up the road, however there are various signs which indicate no trespassing, and the authorities will be notified. It is not wise to attempt venturing in to this area, because of the sensitive nature of the residents.

The road is maintained jointly by the city and county. It is thus a private road maintained at public expense.

A fork in the creek

Penitencia Creek has two main sources which converge at the “horse bridge” near the uphill end of the creek trail. The fork from the north is Penitencia and originates from Cherry Flat Reservoir. Alum Rock Falls are about a quarter mile from the fork, however they have been officially off limits for a few decades because the city of San Jose has not rebuilt the washed-out trail. The creek from the south is Arroyo Aguague and originates in Grant Ranch. Although a couple miles of the creek are within the park, this area too is off limits to visitors.

Activities & Current Updates

Construction of facilities near entrance

Near the entrance parking of the Park, a new entrance and facilities are being planned to be built with planned completion in summer of 2008.


37°23′52″N 121°47′59″W / 37.3977168°N 121.7996751°W / 37.3977168; -121.7996751[2]


  1. ^ Gudde, Erwin; William Bright (2004). California Place Names (Fourth ed. ed.). University of California Press. pp. 10. ISBN 0-520-24217-3. 
  2. ^ U.S. Geological Survey Geographical Names Information System: Alum Rock Park
  • Information from the San Jose Regional Parks brochure for Alum Rock Park (revised June 2002) and from informational signs throughout the park.


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