The High Valley Road runs most of the length of the ridge from High Valley to the Bartlett Springs Road. The high point is towards the northwest end of the ridge less than 2 miles from Bartlett Springs Road. The road is well graded and passable to all cars albeit quite dusty in places during the dry season. This makes for a moderate but long walk up the road from High Valley or a short one from Barltlett Springs Rd. to outstanding views out over Clear Lake, Mt. Konocti and the Mayacamas Mountains beyond.
From Bartlett Springs Road From the junction of Hwy. 53 and Hwy. 20 go west on 20 14.5 miles along the lake to Bartlett Springs Road. Go right on Bartlett Springs Road (passable to all cars) as it winds and switchbacks up to the junction with High Valley Road at 5 miles.
This involves about 14 miles round trip and 2,100' foot gain.
From Bartlett Springs Road: From the junction of Bartlett Springs Road and High Valley Road hike 1.5 miles to the forested high point up to the right. This is 3 miles round trip and about 500' gain.
Of course you can drive the whole ridge, get out, enjoy the views, have a picnic and be done with it.