Canyons are inherently risky. Flash floods occur without notice on sunny days. Technical skills & surrounding topography knowledge required yet does not eliminate risk.
I'm sure we're nearly there!!
Yep, it is the upper lower San Andreas canyon, as distinquished from the lower Lower San Andreas Canyon. The Canyon cuts in the Sacramentos run from the desert up to the ridges and peak over 9,000'. The west side of the mountain is bisected by Westside Road (FR 90)... running along generally between 7000' and 8,000' elevation. Normally, the trails split naturally upper and lower relative to Westside Road... except for San Andreas Canyon. Unlike it's proud brother canyon to the immediate south, Dog Canyon, and really all of the other drainages on the west side, there is no trail that allows egress on down to the desert base. Not only is there no through trail, the canyon access is effectively halted at the 6600' level by a waterfall and adjoining vertical, if not overhung, cliffs. You could repel down with enough rope, but why bother.
There is an old trail coming up the drainage from the desert floor... topping out on the map some ways below the waterfall, but there is enough drama and moment to be found above the falls. Make your day out of what is to be found up above.
There in no trail nor any real trailhead. Effectively this is an off trail hike that takes the term bushwhacking dead serious. The hike begins anywhere you decide to make your way off Forest Road 90E... moving to your right down into Lawrence Canyon. It is all dense scrub, denser the further you travel down FR 90E, so it is likely a better idea to commit to heading on down within the first mile off Westside road. Pick an elk trail and angle down... down is all you have to be concerned with... down and more down. Eventually, you'll hit the bottom of the drainage, narrow and overgrown if you headed down very early. Lawrence dumps into San Andreas after a short while, and even before then it turns into a pleasant riparian highway. Most of this upper drainage and all of the coming sections are flow with some gravel over mostly exposed bedrock, and with luck you'll be walking through sections that are best described by that old term "babbling brook". It is nice. The vines, shrubs and hardwoods create a parklike canapy that makes this ever winding and twisting stream/trail just a variable delight.
As you work your way down stream, the scope of San Andreas canyon never comes into play until you reach the terminating waterfall. Until then the walls immediately surrounding the stream bed are either solid tree lined or rock escarpment rising 60' to 150' vertically, blocking off views of the broader canyon expanse, and giving a very intimate effect to the hike. Once at the waterfall you will finally glimpse the towering cliffs and the full breadth of the upper canyon walls.
Of course, if you do more like I do than like I say, you will have not entered the canyon from the first miles of the forest road in the upper portion of the drainage but instead followed FR 90E to it's far terminus, and then moved even further west and around the ridgeline before starting your descent into the canyon bottom. This approach has the added drama of false descents, terminating if vertical wall cliffs blocking further progress, requiring backtracking and re-climbing back up to the mesa bench, then further lateral movement back up canyon moving through brush so dense that the 60 degree slope you are traversing/descending poses no real threat of falling because at any given time at least three body parts are securely bound into the flora. There was a saving grace to that hour or so of impossibly dense bushwhacking. I realized at one point that it was impossible for the plant growth to pose any thicker barrier... it could get thornier... it could not get denser. That was somehow reassuring.
I did get lucky in one respect... my chosen maiden route did drop down and come out on a bench 100' above the river bottom, and yet within a few hundred feet of a drainage cut that allowed me access to the bottom of the canyon. I was really hitting it nearly at the waterfall, just a few minutes walk down to that point. I was additionally rewarded with the pleasant discovery of the virtual roadway the riverbed provided for exiting the canyon... I worked my way up into the Lawrence canyon drainage and followed it until a promising elk trail exited to the right and up. I think/feel that the longer one stays in the drainage, the better. I'll check that out on another day. I had this day parked up on top of the mountain at the Solar Observatory, hiking trail 234 down to access Westside road, so I did not think I needed more exploratory.
This hike/trail is what you make of it... it is worth the effort. You will have privacy, views, intimacy. It is a great area to get lost in for a few hours.
Let someone know where you plan to go, and when you plan to be back... otherwise, they'll never find you in this mess! Don't get caught down near the waterfall if it is raining much on the peak... that would be one hard landing if you're swept over the edge.
WARNING! Hiking and outdoor related sports can be dangerous. Be responsible and prepare for the trip. Study the area you are entering and plan accordingly. Dress for the current and unexpected weather changes. Take plenty of water. Never go alone. Make an itinerary with your plan(s), route(s), destination(s) and expected return time. Give your itinerary to trusted family and/or friends.