It's quite a long haul up there. I think the bridge is at about the 43km marker. Turn left, go across the bridge.....just after the bridge there is a small road leading down toward the river.....check the road before going down to make sure the vhicle you are driving will make it back up. There are a few nice spots to drop a tent down there. The first summer that I moved to BC we camped at the end of that road (about 200 yards down) right beside the slow moving side channel. the side channel is a good spot to toss some spinners for doliies, cutts, and bows. I have caught all 3 species in one weekend there, as well as hooking into 2 BIG coho in November while targetting trout. A tonne of fun that was on spinning gear.
I have been told that the Ashlu and Elaho Valleys have the closest Grizzly Bear population to Vancouver.....so be careful. I have never seen one, but have seen some prints in the mud of Squamish River backchannels that would be way to big for a black bear.
Cheers.....
Peter