At the Rainbow Road exit off I-80. On the South Yuba River. Super nice place, even if the freeway is 200 yards away. If you're familiar with the Bay Area to Reno run on I-80, there's a place where it crosses some beautiful rapids. This is about ½ mile downstream from that.
When Silver Lake Campground is full, this parking area a few miles down the road is open for camping. It's just parking and a few [picnic tables, but it's quite scenic.
I have used the hot springs without camping, and lately I have been camping without soaking, so I'm breaking them into two spots. This is the camping spot.When the hot springs road turns left, take a right and park at any of the several rough camping spots. The hot springs is a little less tan a mile further on.
The springs at Grover gurgle out of the hillside into a beautiful U-shaped alpine meadow. So it should be a groovy, enchanted place, but sadly it is managed by the State Parks system, who do their darnedest to make it prosaic and institutional. The pools are a couple of rectangular concrete tubs - a big one with lukewarm water, and a shallow (3 feet) one, maybe 40x20 which they keep at a pleasantly toasty 104°. You can look over the fence on the uphill side and see the water burble out of the ground and down a sluice to you. There are showers and cubbyholes to store your stuff. There is a campground, which I have never used since it's CA State Parks expensive and there is boondocking three miles down the road.
California state park campgrounds are too expensive. If you're paying for beachfront that's one thing, but parking my van on a level spot in the woods with a bathroom for $35 does not work for me. The fine young man at the entrance kiosk told me that a couple of miles back on National Forest land, the signs saying "Camping 14 days max" also signify "OK to camp here tonight". So that's what I did.
In the style of Inyo Forest campgrounds(*), this one is hard to find(**) and kind of shabby and rough, but it's in a really beautiful location. This one is on Lee Vining Creek, in the aspen/pine forest on top of the glacial till. It's the first campground on CA 120 west of Mono Lake heading up to spectacular Tioga Pass. It's pretty cool. It's very popular with fishermen. (*) Except the Inyo campgrounds around June Lake/Mammoth. They are run by a concessionare. They are a little nicer, cost twice as much, and have three times as many rules. (**) There is an arrow for "camping", but you must turn off the road to see the "Lower Lee Vining" sign.