This is an amazing route to the top of Mt. Diablo, starting in one of the Bay Area's best kept secrets - Pine Canyon in Castle Rock Park, Walnut Creek. It's 2 1/2 to 3 hours up and 45 minutes down.
Ride up Stage Road
through Pine Canyon with the 150ft - 200ft sandstone cliffs on the left on a trail that switches back across Pine Creek five or six times - it's lots of fun during the rainy season when the streams are in flow.
Follow Stage road up the rough climb to BBQ Terrace, through the beautiful secluded canyon, eventually making it up to South Gate road. The views are a welcome distraction with wide sweeping corners and amazing views out to the south and Livermore valley and out west to the Sierras.
At the top, enjoy the luxury of feeling superior to the folks who drove their car to the top. Take a break at the small museum to lear about the geology and wildlife that you passed on the way up before heading down the road (only 2 miles this time) to Juniper Camp. From here it's back onto fire roads to ride red dirt trails down the western ridge before racing down Burma road.
The ride ends with an amazing descent culminating in a pucker-inducing 44 degree gradient down to Northgate Road.
Be wary of riding in the rain or one or two days after rain. The trail up to BBQ terrace turns into adobe and will build up a layer of sticky clay on your wheels until they build up and jam on the frame. If you get off and hike your bike then it will build up to 2" and you'll be walking on platform shoes. Think it's an exaggeration - then try it.
Plenty of creek crossings during the wet season - expect wet feet.
Take care on the Burma Road descent. Make sure that your brakes are in good working order. Watch out for minor rock slides onto the road on the swooping corners too.
From Castle Rock parking lot, follow the paved road up into the park. Pass the swimming pool and baseball field on the right before getting onto the gravel road before the real trail starts. Take a short climb up an exposed sandstone slab that will bring you around the corner to an amazing view of pine canyon and the rock formations on the left.
From there, follow the relatively level Stage Road
as it runs along the middle of the canyon and the stream switches back and forth across it multiple times.
Keep going until you reach the East Bay Regional Park boundary, where there are a couple of picnic tables under the shade of trees. The gate marks the park boundary with Mt Diablo state park on the other side. Make sure that you close the gate properly - the state park is mixed use land and there are often cows grazing the other side of the fence. After this point the ride gets interesting...
The branch at the end of this segment heads up to the left and is a short steep section up to north gate road. If you're doing the Burma road loop, this is where you come down from the top and meet up with Stage Road
This fireroad trail starts getting steep with some uphill, then a short nice swooping downhill and and another stream crossing before heading up into the trees again for the final climb up to BBQ terrace.
The last section of the climb is rough going - it's not technical just steep and drawn out - you know that you're getting close when you see the fence in the distance just below the ridge. Beware the upper section of this trail is adobe mud - in the rain it will accumulate on your tires and build up until it starts to jam in the frame, and when you hike it will build up on your shoes.
Eventually after much pain and agony, you'll pass through the the group camp and hit the Road. From there hang left and head on up to the ranger station, and it's road riding to the summit. Follow the road as it switches back up to the southwest side of the mountain towards the summit. You'll gain elevation quickly and the riding isn't too painful on the paved surface. Be careful of preoccupied drivers the last quarter mile or so.
Leave the summit (taking the right fork down). Be careful in winter - this section is shaded and on frost tends to stick in the shade on this side of the mountain - adds an extra slipping hazard.
Once you're past the lower parking lot, belt down the road to juniper camp. Take the corners carefully and don't let your speed get away from you.
Follow the swooping corners as the trail switches back and forth down the mountain along Long Ridge.
After about 1.5 miles, make sure that you follow the main trail to the left and don't take the short branch to the park boundary. At the junctions just go straight. Follow the fire road (red dirt) along the ridge before it switches around the end of the ridge and starts heading back down the northwest side of the mountain. The main trail is obvious - don't take the fire road to the right when you reach the cow watering trough - head down the rocky technical fire road branch to the left.
When you see a singletrack off to the left further along ignore it - blast down the fire roads. There are one or two short up-hills after a little stream that you'll have to pedal up, and one washed out streambed that is quite technical - but other than that it's a fantastic downhill breeze.
After a short uphill on a mound (that your momentum will get you almost to the top of) comes the insane half mile, 44 degree pitch descent. BE CAREFUL - it's a steep, loose surface when dry and there's a road at the bottom. It comes in two short sections DOWN, flat, then DOWN again.
Cross north gate road and follow the fire trail, taking the first branch left down to pine canyon again dropping you off at frog pond again. From there hang right and head back splashing through the streams until you get back to the parking lot.