I only made it up the first 2 miles before it got too hot to continue. This is a moderate to slightly strenuous hike. Many switchbacks help traverse the steep terrain, but several large "steps" have been constructed that were a stretch for me and I'm 6'5". Go early in the morning or pick a cool, overcast day. The heat gets sucked into the canyon once the sun comes out, but as the single-track trail winds back and forth, you get a really nice breeze as it comes back out to the open-face part of the mountain. The trail actually exits out the West side of the little park setting by the Parking lot, just follow the road up towards the mountains, and veer right after the dam so as not to enter the private Retreat area on the left. When I hiked, there was some large orange netting marking the boundary. I don't reccommend checking out the short 1/2 mile jaunt to the waterfall, unless it's been raining a lot. It's more of a hassle climbing rocks, etc. Just climb the hill, and it eventually connects to the Mt. Wilson Trail if you have the time to reach the peak.
This is a great hike, and I will definitely go back on a cooler day to hike the whole distance.
Also, this is not a highly used trail on weekdays, so if you are looking for a nice quiet hike, go during the week.
Flush toilet is on-site at Parking Lot. Picnic area as well, with BBQ stands.