Found this place completely by fate. A friend and I were driving down the highway and the car behind us was driving within a couple feet of my friend's back bumper. I told him to pull over and let the car pass and we pulled right into the parking lot of the Feather River Hot Springs. We have done a decent amount of hot spring hopping, but had no idea this one was on our route.
We called the number on the sign, payed the day fee, and enjoyed the hot springs for a couple hours before getting back on the road. I thought the setup on the river was genius, and if I remember correctly, I recall the tubs were piped by two separate sources, one which was a sulfur spring and the other lithium. I hope I'm not confusing this with another hot spring I visited! Either way, I thoroughly enjoyed these hot springs and will be sure to stop there again.