TL;DR version - A nice four pointer and a good place to do a leisurely activation. Enough of a hike to feel like the one worked for the summit. Good APRS coverage, okay ATT data coverage. QRM on small portions of the CW frequencies (40/30/20M). Get there early or risk not finding a place to park and don't forget your WA Discover Pass.
The details - I arrived as the sun was coming over the hills to the east, around 730AM. There were no other vehicles in the parking lot but this is a popular destination for mountain bikers; arriving later in the morning may mean not finding a spot, at least during the summer. A Discover Washington Pass is required to park and you cannot purchase a day pass on site. Google maps provided accurate directions from Portland (YMMV).
From the parking area, it is a steady, mile-long climb (about 600') on a rough road up to the summit. There are a couple of places along the way with views to the west but the summit itself is pretty much view-free. When you arrive at the top, you will find a couple of fenced-off antenna towers and a flat, tree-free space. There's a heavily used path due north of the tower complex and solid tree cover on the entire east side.
I set up in the northwest corner of the open space, near a group of large rocks and a single pine there that both provides some shade (at least until noon) and a place to hang one end of a wire. Setup was easy and out of the way of the bikers coming through, so it is a good spot for a longer activation. I put up an EFHW in inverted-L form and used my FT817.
Interestingly, the first signals I heard on 40M were the Chinese broadcast stations around 7.2MHz. Conditions were generally pretty good. I heard stations in a broad sweep down to Texas and east as far away as WI. There was significant QRM, S7 to S10, a sort of "structured" 5KHz wide signal, in the lower end of the CW bands on 40, 30, and 20M.
APRS coverage is quite good and about half of my beacon transmissions got repeated back to me. I did not try messaging but given the station list I saw, it is probably workable. I was able to spot myself but generally ATT cell service was spotty and data only.
I made all of my contacts on 40 and 20 meters as my HT was, apparently, on the fritz, though I didn't figure that out I was on my way down the hill.