Collecting a light dusting of snowflakes on the coldest days of winter, Mt Diablo (3849ft) is over 1200ft higher than Mt Tamalpais in Marin County. On a clear day (early on a winter morning is a good bet) the views from Diablo’s summit are vast and sweeping. To the west you can see over the bay and out to the Farallon Islands; to the east you can look out over the Central Valley to the Sierra Nevada.
Most easily accessed from Danville or Walnut Creek, the park is threaded by over 50 miles of hiking trails. You can also drive to the summit, where there’s a visitor center.