Sent up on Saturday. I was about 4" under the third set (each set is about 48" from center of 4x6 to the next 4x6, although the top set rests above ground. But for simplicity, 4 ft per set).
This is anprettynrocky layer. Got a good part of the bottom down to:
I have a ladder, so I'll need to move it to get the whole bottom. As a reminder the inside dimensions are 30"x48", so the full hole is ~40" (30+3.5+3.5+1.5+1.5) by 58. Realistically I need space to to push threaded bolt down and tighten nuts, so I usually go down ~54 inches before I put in a new set of lumber. It seems quicker to jump up a set and pull up a bucket in 4 ft increments rather than use the hoist. I save the hoist for lowering and raise the hammer drill, as it's awkward to climb a ladder holding it.
The handheld hammer drill is great, but it does struggle a bit when I get a shelf of solid rock. Next time I may use the full size jackhammer. The handheld is really great at embiggening the walls. I have a tendency to want to go deeper and then have to spend a trip or two getting the width right. The last 2-3" have been pretty hard. Usually it's partially calculated caliche (my heat guess I was a business major) where the rock comes apart fairly easily (resists a shivel, but a rock hammer splits easily). This layer had actual quatz:
So prettty tough stuff. Mule is in shop for its first ever annual maintainance, so I didn't haul off the bigger rocks and gravel. Next time I'm up I've got a good dozen buckets of abiut 1/2 to 3/4 gravel that I'll spread out on "road" and another half dozen buckets of larger rocks I'll throw down a ravine.
My aim is to build it up enough to drive the mule across. That's the property fence line, and my current path cuts down a hill. This route would be more gradual.