Blackhawk is my favorite trail in Mt Madonna County Park. It's a steep trail that runs up Blackhawk Canyon, which is full of redwoods, boulders, and a lot of rapids in the winter. The lower portion has been closed for most of the last decade, but it just recently opened after they cut a new cut off where it was washed out to the Ridge/Contour trail junction. This cache is located at the bottom of that cutoff trail and is great resting spot about 1/2 way. If you came up from Sprig, you probably need the rest!
I am really impressed with the work the park did in building the cutoff trail, and some of the amenities... like repurposing some large chunks of wood into a picnic table and benches! And they created a seating area by embedding a couple of flat rocks they found further up the trail into a log.