I got to the HellsGate Trail in a sedan via 260/405, and dayhiked to the confluence,
about 7 hrs roundtrip. There's a pretty narrows, about 1/4 mile long, but the water
was painfully cold - an air mattress would have been nice. Most of the trail is
along a wooded ridge, then about 1 mile across a broad meadow, and the last
100 yards is steep and loose enough you want to test your foot before trusting it.
At the confluence, there was debris 15 ft above the water line, and the canyon
there was 200 ft wide, so flood water exiting the narrows must be an awesome
sight. I only saw one good camp site, which was occupied by a guy who was
fishing from a ledge halfway up the cliff in the narrows.