Aha! Looks like that old concrete structure supported the old old bridge for logging trucks to barrel across! Thanks for this photo, really interesting. Now, I have a map from 1978 which marks the lower falls, the upper falls, then Burke falls and finally the old Burma Bridge in ascending order. Tried to upload the map but it's too big. Have googled Burke falls but no info shows up. Was just curious if anyone has heard of them. On my map it looks like the "lookout" area on the west canyon trail is right across from these falls. I'm assuming the "lookout" is the spot where you can see Gold Creek from high up. You look up the creek from this spot. I'm going to try to look across the creek next time I'm up at the "lookout" to see if i can see any sign of these Burke falls! Trees may hamper the view however.
I was under the impression that Burke Falls is the official name for Upper Falls, although I have heard other references to a third waterfall. Judging by Google Maps, it seems unlikely to be between Upper Falls and the bridge, since the river is fairly flat there. I've attached an image from my map showing the area that you might be able to match up to your map based on bends in the river.
I'd also love to see the 1978 map, maybe you could upload it to a site like Imgur
if it's too big to attach here?
Alhike: After crossing the bridge to the west canyon side, the logging road curved towards Hikers Beach before turning up to Alder Flats (forming the old hiking route, and the "Descent into Madness" trail). Some old maps appear to indicate the logging road also went up along East Canyon as far as the 5km mark (past Hikers Beach) before crossing to the other side for a short distance. You wouldn't happen to know anything about that?