Harbin Hot Springs is a popular resort up in a canyon northwest of Middletown. Harbin Mountain is the high point above the hot springs on a ridge coming down from Boggs Mountain. It can be approached from Harbin Hot Springs, Boggs Mountain or Big Canyon.
This is a very pleasant hike from Big Canyon to a fine viewpoint. Especially southeast over Long and Collayomi Valleys to Mt. St. Helena.
It is approximately 4 miles and 1,400' el. gain round trip.
There is a trail out of the Harbin Hot Springs grounds but I believe you have to be a guest to have access to the recreational activities such as hiking the mountain from their side.
It can also be approached from Boggs Mountain but those routes encounter private holdings and are questionable.