First time climbing to the Diablo Summit and it was a bit of a butt-kicker. Started off at Mitchell Canyon and went counter clockwise to the summit. There were lots of breaks as the trail had some mostly vertical inclines. It was also very wide going up so lots of room to pull over. Stopping at the visitor center for Gatorade (or even ice cream) was fantastic. Going down the path was gravelly for probably about 5 miles. It was a challenge without trekking polls! The last little bit of the trail was gorgeous however and a nice way to end. Post-hike meal was Mona’s Burgers, which was delicious, highly recommend for post-Contra Costa hikes.
Other logistics: $6 parking fee at Mitchell Canyon, cash only. There was a gate monitor when we arrived. The parking lot was incredibly full but we only saw people at the trailhead, the trails themselves were pretty open.