The hike begins and ends at a trailhead in the middle of a very posh residential area: huge, multi-million-dollar McMansions set in the hills. The trails often pass above them, which means you get to spy into their back yards.
We went with the bahiker.com suggested hike again, and again it was a good 'un; although it actually spends a lot of time outside the park boundary, taking the Alamo Trail along and below the South edge of the park, and heading into Mount Diablo State Park.
We stopped to eat our picnic at China Wall, a rock formation which the pictures don't really do justice to; it's a ridge of rock running hundreds of yards along the hillside, and what the photos don't show is that behind it are further ridges of strata: a whole chunk of mountainside turned on its side and eroding out.
And it's full of ground squirrels: Beechey ground squirrels, so common throughout most of California that they usually seem to simply be called California ground squirrels. We came across more of them on Stonegate Trail.
The park leaflet mentions bobcat and coyote; no sign of either, but there were some distinctly catty footprints on some of the trails.
We took the suggested extension to see more of Castle Rock, a big orange rock formation on the flank of Mt. Diablo: but what bahiker doesn't tell you is that, although it's an extra 2.25 miles, it's not a flat 2.25 miles. It heads down a ravine, which was nice, as in the cover of the ravine the trees are still green and fresh; out on the hills, the oaks are leafless and blasted-looking. But the route back up was a stiff climb up a steep dirt track.
The section of the hike within Diablo Foothills is easier — the hills are more rolling — but also less interesting with less to see; although there's a good view of downtown Walnut Creek from the junction of Stonegate and Foothills trails.
A good day out, and taking a picnic made it; Christmas day leftovers taste much better outdoors with a mountain view.