Angwin is a Seventh Day Adventist town. If you do the ride, do not plan on buying anything on Sundays, the town is closed. When you hit the town, follow the signs to the airport and park, the trail starts here. The trails are on this property, and to give you an idea, they had a race there a few years back, and just the one loop for the race was over 26 miles, and this barely scraped what this place has to offer. Do not go alone, you can get lost, because the place is thousands of acreas of forest.
How to get there:
If you know where Napa is, continue north on the Silverado Trail (a road) till you see the signs for Angwin (thirty minutes or so). Once you take the right turn here, it will take about fifteen minutes till park time.