We were able to make it to 0.5 mi from the trailhead in a stock crosstrek with all terrain tires. Beyond that there is a washout that is about a foot/half foot clearance. The trail is slightly grown over at the first switchback section but easy to navigate. First switchback section is exposed/hot and sometimes directly UP.

Otherwise this trail is gorgeous!! Saw one other group on a Saturday afternoon. Wildflowers still present. Panoramic views at the top. Short and sweet but the elevation gain makes your workout with most in the first mile, then at the very end for about 0.3 mi. We did this with our dog, always recommend leash due to the exposed ridge lines and critters.

Some POS has broken into the fire lookout and left a good amount of trash :( I attempted to close the door but it had been kicked in.

Road: after the last turn there are a few washout points that make it impossible for low clearance to pass. Saw many park further down the road.

Bugs: I thought they were fine until I got home and was covered in multiple bits.

Trail: lots of tall overgrowth to walkthrough but passable. Some areas are narrow and hard to see your path. Wildflowers were still in bloom, too early for huckleberries.

This was a great hike.  It is a bit of a grind the first mile as you climb the first slope but the views are worth it.  As others have noted, about .6 from the trailhead the road is impassible for anything other than high clearance vehicles (i.e. Jeep Wrangler).  I tried it in my Hyundai Palisade but ended up getting stuck for a worrisome minute and I didn't even get to the really bad parts.  A normal SUV will not get through, you must have a high clearance vehicle.  No snow, no bugs, VERY dry.  

I wrote "Bugs were not too bad" because we saw a preying mantis so bugs were awesome, actually.

Leaving a quick trip report for two reasons. One, previous trip reporters noted they parked ~1 mile from the trailhead. Knowing they did not make it all the way, I resolved to see how far I could get in my Prius. I stopped two switchbacks shy of the trailhead, right where the road looked like it might become an issue. While walking to the trailhead and evaluating the road, I think I made the right decision; other cars/drivers might get closer to the trailhead, but I feel confident that anyone can safely reach the switchback where I parked. After returning home, I measured the spot using Caltopo and confirmed it is almost exactly 1 mile from the trailhead. I've attached a screenshot below so you can see exactly how far I got.

Two, WTA's written directions are great and will get you right to where you are trying to go. That said, DO NOT simply click "Open in Google Maps" and follow those directions. FR 4308-120 does not appear on Google Maps, so the algorithm will try to direct you via FR 4312, past a different trailhead for Thorp Mountain (via Thorp Creek and Thorp Lake). In other words, you will get to a trailhead, but not Knox Creek. The combination of WTA's written directions and the (accurate) maps on Caltopo helped us get to where we were going.

Arrived around 10am on a Saturday. Our honda fit did fine till about 1mi from the trailhead where, as others have noted, there's a very large gulley in the road. We didn't even attempt driving over it, just parked where there was space on the side of the road and walked. Saw no other cars, although on the way back it looked like there were some fresh tire tracks showing that someone had made it past.

The hike was outstanding. Great views on the ascent up to the ridge trail, and then even better views going up to Thorp Mountain and at the lookout on the peak. The Knox Creek trail was steep and narrow and sloped sideways at times but we had no real trouble.

We encountered 2 bears about half way up the Knox Creek trail. A smaller one we guessed was a cub, and then a larger one further away that we assumed was its mother. The cub ran off and the mother watched us until the cub was away and then they both left.

We only encountered 3 other hikers + a WTA work crew all day. My watch said 6.4 mi and 2264 ft, including the extra mile we walked on the road