I started at the Yacolt Burn Trailhead and ran clockwise. I ran alone, and carried 1L water, plus a water filter and all snacks. Hopped over 4 snakes, got stung by a wasp, stepped into an animal hole, and lost my way a few times, but I made it around! I started late into the morning and it got pretty hot. I drank 3L of water and had to stop to filter 2-3 times along the way. The first was at Hidden Falls. There are plenty of creeks along the route, but you do have to get off trail to get to them.
I would describe this trail as quite technical! It's incredibly rocky in all areas except the parts under tree cover. The trail is pretty well marked throughout, but sometimes the connection is hidden and there are many unmarked trails in the same area. Also, depending on the time of year, this trail can get REALLY overgrown, and that would make it harder to see the trail connections. As others noted, it is easy to get off trail in a few intersections in particular, and best to familiarize yourself with the intersections and keep the route handy when you run.
I love the Yacolt Burn area, and this is such a cool trail in the various seasons. Was a lovely day out there!