We were on vacation in SLO county in early July and decided to try Big Falls since we have a vehicle suitable for the 18 water crossings necessary to reach the trailhead. This old LA Times article is as good as any. I was surprised how many residences and, it seems, pot farms there are a good ways down Upper Lopez Canyon Rd. There's a bunch of signage saying everything is private and you can't stop until you get to the trailhead.
The trail was in good shape and there was a good amount of water. I saw a Yellow Mariposa lily.
In this pool we saw a TURTLE! Presumably a Southwestern Pond Turtle. He was too evasive to photograph. Every few minutes he swam out a little bit and then went an hid. Definitely the highlight of the hike.
The falls was fine but my photo isn't great. We hadn't seen any other people, but as we sat snacking 3 others arrived and dove right into the pond. They told us they understood the trail is very popular on weekends with Cal Poly students.
We also tried Little Falls trail and did see some water flowing over rocks, but we might have turned back before the falls if it was flowing. Continuing would have involved quite a bit of poison oak.
We thought we were all badass driving down there, but when we exited we found a RAV4 and a CRV parked, and we passed a minivan (!) on the way out.