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Full loop of park - PG&E trail to Black Mountain return on Chemise and Rouge Valley.
Description from http://www.redwoodhikes.com/Skyline/PGE.html
Rancho San Antonio is one of the Bay Area's most popular parks. On a nice summer day there's a continuous stream of people on the main road to Deer Hollow Farm, and even on the challenging 8-mile PG&E Trail there's a group of hikers or joggers every 1 or 2 minutes. It's often said that the park is overcrowded, but the activity (along with the wide, well-maintained trails) also help to make the park feel safer and more family-oriented than the more remote parks.
It's easy to see why the park is so popular: it's just a few minutes' drive from most of Silicon Valley, and although it doesn't compare with more distant parks to the west of Skyline Ridge, it's quite an enjoyable place to hike, with a mixture of woodland, open grassland, and some very nice panoramic views of the Bay Area. The park is also large and well isolated from the nearby suburban neighborhoods, so it offers a real escape from the city without a long drive.
Even though it's partly wooded, Rancho San Antonio, like most of the parks in the area, can get really hot and unpleasant in the summer. While everyone has different limits, personally I can't hike there when the forecast high for the day is above 85 degrees.
The PG&E Trail loop is a good workout with some great scenic views and is one of Rancho San Antonio's most enjoyable hikes.
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