Gibbon Mountain is little known peak near the Gordon Hirabayashi Recreation Area (also known as Prison Camp). It’s not a long hike but nor is it a particularly easy hike. It’s never technical, but there’s a lot of walking through long grass with no trail to follow, and several false summits before you reach the final peak.
Drive up the Catalina Highway, past Molino Basin, to where the road briefly flattens and you can turn left to the the Gordon Hirabayashi campground. If the gate is not closed, drive to the end of the dirt road, to the trailhead for the Arizona Trail (otherwise, it’s a short walk down the road to the trailhead.)
Follow the sign for Sycamore Canyon for less than half a mile, until you see three old sections of pipe on the left. (If you see three pipes on the right, or a pipe across the trail, you have gone too far.)
Just after the three pipes there’s a very small wash coming in from the left, and just after that there’s a faint trail leading left. (Just after this trail, there’s an Arizona Trail sign on the main trail, or at least there was in December 2021.)
Follow the faint trail left and after a short while it becomes much more distinct. Follow this easily to where the hill starts to get steeper. Now the trail disappears and you’ll have to basically bushwhack upwards to the ridge. Once you reach the ridge, you can see another ridge leading leftwards. Head to this and follow it past various false summits until you reach the top of Gibbon Mountain, where you will see two big cairns, and a great view of Thimble Peak.
Since there’s no trail once you reach the steeper part of the hike, it’s worth looking back periodically as you hike so you can tell which way to go on your return.