Morgan Territory Regional Preserve offers stunning views of Mt. Diablo from the East. Highland Ridge lookout is a great summit to view Mt.Diablo. This is the Strava trail for reaching Highland ridge.

https://www.strava.com/activities/5029213313

The parking lot for the trailhead is a couple of miles from the staging area parking lot. If you keep driving on Morgan Territory road for a couple of miles, you will see a small pullover where there is space to park 3-4 cars at the trailhead.

You get to see great views of Mt.Diablo almost immediately on the trail.

Early spring is a good time to catch poppies blooming.

The view from the Highland Ridge summit is absolutely stunning, you have sweeping views of San Ramon and Danville and Dublin hills.

Morgan Territory offers multiple backpacking campsites as well. I have a 2-3 night trip planned in the area hiking towards Mt. Diablo and summitting Mt. Diablo. I should attempt it early Spring some time.