A reasonably nice city park, good viewspot at the top ("Eagle Rock"). Mostly dirt road, with some short sections of technical downhill singletrack. Can get a little crowded due to proximity to the city There's a big "Alum Rock County Park" sign up on the cliff; enter the park to the right of the sign, and go up the trail next to some rough wooden steps.
Follow the trail on up until it goes onto the main (paved) road into the park. Go up on the road for about a hundred yards, then a sharp left onto dirt ramp; at the top, turn sharply right onto a dirt road above the paved road. Eventually, it crosses a bridge over the paved road. Continue up to the "Youth Science Institute" (there are restrooms and a drinking fountain here). [Optionally, go on up the canyon to get the full sulphur effect of the "Mineral Springs" that made this park a famous resort many decades ago. Return via the same route, to the "YSI" building. Across the paved road from the YSI, the "North Rim Trail" starts up the side of the canyon. (It's paved here.) Climb up it, continuing along the north rim of the canyon. Shortly, the pavement disappears and there is a gate to go around; the trail snakes up and down (but mostly up) towards Eagle Rock (you can recognize it by all the antennae on it). One turnoff to the right is labeled "Loop Trail" -- worth avoiding unless you're into steep climbs. A couple of spots along the main trail get pretty steep -- you can avoid the second one by staying left as the road forks just at the bottom of that steep part, then taking the switchback right turn that goes up to the top of that part. Once you get up to Eagle Rock (elev. 790'), take a break. Take some pictures. To get down, take mostly right turns. At one spot, you're headed West (out towards San Jose) and the trail has a steep branch down to the left, but also continues a lot less steeply, sorta straight. You can see where the steep left branch goes down to another trail. At that point, take that steep left branch -- the other just goes out to a small place where a couple of goats live, and peters out. That steep descent is the trickiest technical challenge on this route. At the bottom of that steep left branch, turn rightish onto the trail that stays just above the paved road. There's one nasty down-and-up right turn that's easy to miss (but if you do, it just puts you out onto the paved road). Once the trail really puts you back onto the road, go right, down the road about 50 or 100 yards, then turn sharply left onto a small trail that takes you back to the main entrance trail, just above those "rough wooden steps" that were right by the start of the ride.