Alum Rock Park

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Alum Rock Park
AlumRockViewSiliconValley w.jpg
View of northern Silicon Valley from South Rim Trail
Type Urban park
Location San Jose, California
Coordinates 37°23′52″N 121°47′59″W / 37.3977168°N 121.7996751°W / 37.3977168; -121.7996751[1]
Area 2.9 km2 (1.1 sq mi)
Created 1872
Operated by City of San Jose
Status Open except non-holiday Mondays
Classic carved trail sign

Alum Rock Park, founded in 1872, was the first municipal park in the U.S. state of California. Located in a valley 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 valley includes a visitor center, a small museum/animal rehab facility, picnic areas, playgrounds, lawns, sand volleyball pits, mineral springs, lush plant life, woodlands, creek play opportunities, and occasional group camping.

The ridge trails offer views of Santa Clara Valley and of the valley in which the park is located. Some trails in the park are a part of the Bay Area Ridge Trail; the Todd Quick trail connects with the Santa Clara Valley Open Space Authority's 1,600-acre Sierra Vista Open Space Preserve.

Equestrians and mountain bikers have access to some of the park's trails, while others are reserved for hikers only. Cross-country teams from high schools around North San Jose, such as James Lick High School and Independence High, use the park for training and for meets.



Historic Alum Rock Bridge, dating from 1913

Alum Rock Park was originally known simply as "the reservation"; it received its current name around the turn of the 20th century when thenardite-containing rocks near its entrance were mistaken for alum.[2]

Penitencia Creek is properly called Upper Penitencia Creek because it no longer connects with Lower Penitencia Creek, which is in Milpitas. The creek also had a different name until the early 20th century; somehow it began to be called by the name of a different creek located to the north, which was so-named because monks (possibly from Mission San José) would meditate by its waters.


The park in the fall

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 stonework remains, however, as do old support structures for a once-existing railroad.

Natural disasters[edit]

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.

Current updates[edit]

Construction of facilities near entrance

The parking lot just outside the entrance kiosk is once again free - there are self-pay machines that cost $6 per day for parking in the rest of the park.



Grotto stonework around one of many mineral springs

The valley has abundant mineral springs, which were touted as beneficial to people's health. In the late 19th century 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. Due to overuse, some of the springs became extinct, and surviving ones became very weak, producing very little output.


The road is maintained jointly by the city and county. Thus, it is a private road maintained at public expense. However, private residents have access to the road. They enter the park and continue 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. Visitors can also walk up the road, but there are various signs which indicate no trespassing.

Fork in the creek[edit]

One of several bridges over Penitencia 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. 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 is off limits to visitors.

Youth Science Institute[edit]

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.[3]

Animals that are commonly found throughout the park are displayed in the center. There is an exhibit of taxidermy birds that is sectioned off into owls, hawks, seabirds, and waterfowl. Animal remains are set up throughout the center and labeled accordingly. There is a separate room for live animals that are kept in their designated space along with a brief description of each animal. Occasionally, there is a pair of owls that roam free within the room. The staff is helpful and willing to answer any questions as well as provide you with a tour once the appropriate admission fee is paid. Brochures and information packets of plants and animals found in Alum Rock Park are available at the front desk.


Black-tailed deer in Alum Rock Park


The steep sides of the valley are home to many diverse plants 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 unique smell to the air.

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

The most common native species of the park include California fuchsia, California wild rose, black sage, hummingbird sage, and blackberry. Problematic invasive species are star thistle, cape ivy[disambiguation needed], and periwinkle vinca.


Several larger varieties of birds frequent the park, including the red-tailed hawk, red-shouldered hawk, Cooper's hawk, kestrel, turkey vulture, wild turkey, mallard, great blue heron, green heron, Steller's jay, great egret, snowy egret, and California quail. Owls that are native to the park are the western screech owl, barn owl, great horned owl, and northern pygmy owl. The northern pygmy owl unlike most owl species is active from dawn to dusk. Larger wildlife includes black-tailed deer, gray foxes, bobcats, and occasional pumas (mountain lions). There has been an increase in the mountain lion population in the San Francisco Bay Area. Smaller wildlife would include the darkling beetle, Eurypelma californicum (tarantula), black widow, and Pacific tree frog. Two species of lizards that are native to the park are southern alligator lizard and western fence lizard. Native fish that can be found in Penetencia Creek are the California roach and riffle sculpin.

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. Another snake that is native to the park is the California kingsnake, they are nonvenomous and can also be found along the trails.


  1. ^ U.S. Geological Survey Geographic Names Information System: Alum Rock Park
  2. ^ Gudde, Erwin; William Bright (2004). California Place Names (Fourth ed.). University of California Press. p. 10. ISBN 0-520-24217-3. 
  3. ^ Alum Rock Science and Nature Center