To get to Tom's Thumb and back it's about 4 miles RT but those are a difficult 4 miles! Going up it's pretty much all climbing, not much flat hiking at all. And coming back down you have to be REALLY careful about slipping because of all the loose dirt. I slipped like 3 times and one girl in our group took a tumble and skinned her knee, ouch!
Great view at the thumb and a fun hike, but just make sure you are prepared! It's not a stroll in the park. I saw lots of exhausted doggies on the trail, so if you bring yours make sure they are used to pretty demanding hiking.
I love that there's lots of parking at the trailhead and the trail wasn't as crowded as other spots.
Make sure you bring your own water bc there is no water at the trailhead!
If you are looking for a bigger challenge, there are other trails that connect up with the Tom's Thumb trail, so once you reach the thumb you can keep going higher up if you want.