Mountain Trail starts a little within the park. There are a few connecting trails that will lead you to it and the park has plenty of signs for navigation to it. The very beginning of it is next to London Lake where you can see a small cabin, a map, and some other informational signs for your learning pleasure.
The run up Mountain Trail starts out pretty mild but will slowly pick up more and more steep sections. It's mostly shaded until you reach Deer Camp (a little over halfway) where the trees will start to thin out. Eventually, you'll take a hard left to stay on Mountain Trail, ignoring Hayfields Trail
. This is the last push until you reach the top of Sonoma Mountain. An amazing view of the valley is quite the reward on this one.