I have always hiked the Walnut Creek side of Mt Diablo…grassy with trees sprinkled here and there, a few canyons, ponds, and some wildlife. Then I went to the Clayton side to summit the mountain, wow – it was completely different.  I wondered, is this the same mountain?! Both sides are lovely in their own way.  I experienced waterfalls, much more foliage/trees, and more drastic landscapes…rather than the rolling, open hills of the other side.  I went clockwise on the loop, contrary to the recommended counter-clockwise.  I prefer a steeper incline than decline. It took 3 hours to summit from Mitchell Canyon Creek Trail head.  Then 1.5 hours to descend back to the trail head after the summit.  Amazing views, terrific visitor center and history about the beacon (operated every 12/7 for Pearl Harbor). And, perfect time of year for wildflowers!