A decades-long plan to build a 550-mile trail for hikers, horse riders and bicyclists ringing the Bay Area is getting a significant boost this weekend in Silicon Valley, as the largest new section added in four years will be dedicated in the hills east of San Jose at a public celebration Saturday morning.

Roughly 5.3 miles will be added to the Bay Area Ridge Trail, bringing its total completed segments to 337 miles. The new route follows broad open meadows and oak woodlands in the Sierra Vista Open Space Preserve, which sits just east of Alum Rock Park in the Diablo Foothills.

“I would call this a jewel yet undiscovered,” said Andrea Mackenzie, general manager of the Santa Clara County Open Space Authority, a government agency that owns the preserve.

“Not enough people know these places are here. This is right in East San Jose. I want to make the public aware that these places belong to them.”

The 1,676-acre preserve — which has sweeping views of Mount Hamilton, Mission Peak, Loma Prieta and downtown San Jose — gained prominence in May, when its location along rural Sierra Road was the site of one finish line on the Amgen Tour of California professional bicycle race, attracting national TV coverage and thousands of spectators.

The new dirt trail, which will open to hikers and mountain bicyclists, is expected to lure thousands of new visitors to the preserve. Horse riders are allowed on about 80 percent of it, but not on the steepest section.

Construction started last April. Crews graded old ranch roads. They installed signs, rebuilt an 80-foot-long steel and wooden bridge and installed a new 65-foot fiberglass bridge over creeks. Total cost: $193,000, with funding coming from state park bonds and the open space authority, which is funded by a $12 per home annual parcel tax.

Slow assembly

The completion brings the total Ridge Trail miles in Santa Clara County to 78, with 113 miles left to go. In the nearly 25 years that Bay Area parks leaders and environmentalists have been assembling the trail, two counties have proved most difficult for building. Napa County lacks public land near wineries, and Santa Clara must contend with large privately held ranchlands, most of whose owners do not want the trail to cross their land.

“It takes years to acquire the properties, and to design it and piece it together,” said Janet McBride, executive director of the Bay Area Ridge Trail Council. “It’s a slow and steady process, and this is a great example of the fruits of that labor.”

The Sierra Vista Open Space Preserve, opened in 2002, won’t have a full-time parking lot and restrooms for another two years. Apart from special events like Saturday’s, the only access is usually by entering Alum Rock Park and following the Todd Quick Trail to the hills.

McBride noted that Saturday’s trail dedication will add the largest segment to the Ridge Trail in any of the nine Bay Area counties in four years. The last time a larger chunk was added was in November 2007, when the 7.5-mile Pinole Watershed Trail in Contra Costa County was christened on property owned by the East Bay Municipal Utility District.

“We need to start linking pieces together,” said McBride. “Right now there are disconnected segments. It’s at opportunities like this dedication on Saturday that folks can come out and get a taste of the possibilities.”

Stunning vistas

The idea for the Ridge Trail began in 1987 with William Penn Mott, a former East Bay Regional Parks director who served as President Ronald Reagan’s national parks director. With 10 to 15 miles being opened a year now, finishing the entire route is still at least 20 years off.

Marked with blue signs, the Ridge Trail takes in stunning views of the Golden Gate Bridge from the Marin Headlands; San Mateo County forests above Crystal Springs Reservoir; bucolic former ranch lands on the slopes of Mount Hamilton; and the necklace of East Bay parks from Mission Peak to the Carquinez Strait.

It also includes many of the Bay Area’s most venerable parks — the Presidio in San Francisco, Joseph Grant County Park in Santa Clara County and Tilden in the Berkeley hills. The trail passes Jack London’s grave in Sonoma County, John Muir’s orchards in Martinez, the cinnabar mines of New Almaden in South San Jose. It skirts past the summer home of 19th-century cattle baron Henry Miller near Gilroy, and Sweeney Ridge near Pacifica, where in 1769 Spanish explorer Gaspar de Portola first set eyes on San Francisco Bay.

Contact Paul Rogers at 408-920-5045.