From the Campanile, take campus roads/paths down to the intersection of Hearst and Spruce. Spruce is a useful but not particularly enjoyable climb up to the intersection of Grizzly Peak Boulevard and Wildcat Canyon Road. It's used by a lot of cyclists. The road slopes upwards with an average grade of about 5% for about 5km. Total climbing is about 170 meters.
Spruce ends at a 5-way intersection with Grizzly Peak, Wildcat Canyon, and Canyon Road (although the road signs can't seem to agree on whether to call it "Canyon" or "Canon"). Wildcat is straight across the intersection and slightly uphill; we're taking the left fork (not a full left turn) and going downhill on Canyon. Canyon is fast and downhill for about 2km. Near where the hill bottoms out, there's a Y intersection with a parking area over to the left; we'll continue on to the right. Soon after that, we turn left onto Loop Drive.
Loop Drive starts out paved, but soon becomes a wide dirt road, then narrows as it gets away from the trailheads. After winding through a fairly heavily populated area for a while, it turns to the right near a pond, and starts to get into some isolated terrain. Past the right turn we'll probably see mostly cyclists. That's about 2km from the start of Loop Drive.
The trail straightens out and moves into the central valley between the San Pablo Reservoir watershed and the Kensington hills (which is called, surprise, Wildcat Canyon). It's an interesting area, and one that's difficult to see if you're not on a bike. The trail rolls up and down; there's one or two areas you have to be careful, but it's pretty easy riding.
We'll pass a few side trails, notably Havey Canyon to the right. Havey Canyon is a good trail if it's open; it's steep and technical, but it allows for some nice loops. When I rode by it was still closed from the spring rains, so we're leaving it out. After about 5km, Mezue Trail will also split off to the right. Turn right on Mezue Trail.
Mezue Trail is a pretty direct climb from the canyon floor to the top of San Pablo Ridge. There are a couple of very steep sections with loose dirt and rocks; if you want to stay on the bike, keep your speed up so momentary losses of traction don't send you flopping sideways. It's about 2km to the San Pablo Ridge Trail from the beginning of Mezue. Turn right on San Pablo Ridge Trail.
San Pablo Ridge Trail starts out unpaved, with nice views of San Francisco and San Pablo Reservoir. There are a few cattle guards and cow chips to deal with. Cattle guards are pretty easy; just make sure you have enough speed, and hit them orthogonally. Cow chips, just stay the hell away from, those things are disgusting. You'll probably also see some horse shit on the trail, but horse shit isn't bad at all, mostly grass really. If it's in small grassy balls, don't worry about it; if it looks like a demented hot fudge sundae, steer clear.
After about a klick we hit the paved part of San Pablo Ridge Trail, which will take us down to Inspiration Point. There are some side trails, and if Havey Canyon is open you can take that down. As we get closer to Inspiration Point, we'll see more pedestrian and dog traffic, which can be pretty annoying; take it slow. We reach Inspiration Point after about 8km total.
Turn right on Wildcat Canyon Road. It meets up with a couple of trailheads within half a klick.
An alternate intermediate route is to turn right on Wildcat Trail. This is a fairly technical, steep descent for about 1 km, then it levels out some and eventually deposits you back on Loop Road. Turn left on Loop, right on Canyon and you'll wind up back at Spruce. This is a shorter but more challenging route than the one above.
The trail has a notable descent and then slogs back up, with some very steep sections, until it reaches a pass at about 500 meters. There's a steep descent--watch your speed, and get that butt off the back of your seat--and then the trail begins the final climb towards Grizzly Peak. After the steepest section ends, the trail turns to the right and intersects a semi-paved trail; turn right.
This trail leads up to the very top of Grizzly Peak. It's hard to ride on a road bike due to the steepness and the presence of gravel and pine needles, but it's not really a problem on a mountain bike. Well, I shouldn't say that; the thing is still a bitch of a climb, but it's probably less flop-prone than some of the other climbs on this ride.
After a short, steep climb, we reach Grizzly Peak. There's not much there except comm towers and some great views; we'll cool down and then head back down. The descent is another butt-off-the-back drop. Once we get back to where we turned off Sea View Trail, keep going straight. This takes us down to Lomas Cantadas, near the steam trains. This is right near Grizzly Peak Boulevard; turn right on Grizzly Peak to return to Centennial/Euclid/Spruce and Berkeley. Total riding is about 50km.