I did some research several years ago and after talking with the Ranger Burns(I could have his name wrong) the T6 crossing appeared on old forestry maps. It is a couple of mile upstream from the steel bridge where the PCT crosses Deep Creek (about 8 miles upstream from DCHS. The T6 is known now as Crab Flats Crossing. The road is east of Cedar Glen.

See Google Link.

https://goo.gl/maps/PEeUaHdnjcT2

I discussed this with several Rangers over many years because policy can change but this one seems pretty set. They don't really know what the T6 is as a place even though it can be found. They understand it as a principle. Nudity is allowed anywhere in their forest except within a 1/4 mile of developed areas. So it isn't one place, it is interpreted as all developed areas.

Practical advice. Calif law prohibits nudity. It is ignored in these areas but not actually legal. There are overlapping jurisdictions in these mountains. The San Bernardino Sheriff and the CHP both enforce Cal law not Federal FS policy. It is the Sheriff and the CHP who fly in on rescues and general patrols. So if the helicopter is up its good to be aware. I've not heard of them enforcing but if annoyed they could.

The potential parent complaint- so many members of the general public come to the Springs now that many are not happy about the clothing optional visitors. If they bring children they could complain to law enforcement and the legal tangle could be problematic. I'm not saying it's happened but in America you need to have a good lawyer that you will pay for to get cleared. So just keep this remote scenario in mind when kids are around. I generally steer clear to avoid any association with them in a CO area.

Wizard had a lot to say about it several years ago when his daughters were young.

Just my 2 cents to fill in what you already knew.