Actually, I think I found it using the BLM map link.
There is a narrow body of water labeled "White Water." There is a road called White Water Cutoff west of the south end of that body of water, that becomes "Old Morango Road" that runs very close to I-10 briefly then wiggles away from I-10 headed generally northeastward. On the correct scale, there is a set of 16 red outlined squares with a "12" in the middle, and the SW 1/4 are the four small red blocks that make up the southwest quadrant of the set of 16 red outline blocks with the "12" in the middle. That's the area being referenced in that project list that the land description came from. Once you get it to the correct scale it falls into place very easily, and you can see that the BLM land description is very clear. If you get to highway 82 that's to the east, you are too far to the east, if you are at the service road to the west of the "White Water" body of water, you are too far to the west.
BTW, I'm talking about the BLM reference, not necessarily where the start line was.