If JRF actually took no water with them (nothing beyond, say, a liter each) and thought he remembered where McCain Spring was, he was more over-confident than I have yet imagined. I can't imagine going out there (even to just the Salton Sea area, which is more populated) without a *lot* of water. Heck, I carry 5 gallons for my daily 20 mile (one way) commute - because I have been stranded at the side of an L.A. freeway in 115F heat and watched both CHP and local police just pass me by (this was before cell phones - but AAA can take its sweet time getting to a call, that's for sure). I've waited an hour for AAA before.
One hour at 115F is not good. And surfaces (like canyon walls) radiate heat and make it even hotter. I'm using weather station values, which are taken in the shade.
I want to have enough water to also use for evaporative cooling (combined with appropriate headgear).
Anza-Borrego back roads are so remote, I wouldn't go without 25 gallons - or more. I also know that I can't carry more than four gallons (and I'd have to offload most of the stuff from my backpack and carry part of that by hand - so, realistically, I can only carry 2 gallons on a hike that involves scrambling - which the descent down Harper Canyon does). LE has said they have found no evidence of water with the couple (but I don't know if that's just based on the truck - or on reconstructing the entire trip across Harper Flat to Harper Canyon). I try to think what I'd do if I were stranded south of Harper Flat. How much water would I take to make that journey to Old Kane Springs Road, in the hope of flagging someone down? I think I would have gone back the way I came (toward the west on Pinyon Mountain Road to the 52 - the 52 has lots of traffic and, I believe, cell phone service along most of its length. For one thing, it would have been a bit cooler to stay walking at a higher altitude. For another reason, it's in the direction of the closest cell tower (in Julian). Plus, the 52 is the typical route taken by tourists in that park and aid could have been sought.
All I can think is that either they were without water and very desperate OR JRF didn't think it through - it seems to me that it would have been about 6-7 miles to relative safety in either direction - but with more chance of cell/help going due west, back along Pinyon Mtn Road if that's where they were, which I think is the case (see
@Herat's excellent posts).
^Road map of Anza Borrego
The big missing piece is the exact location of the truck - but no matter where it was along 52 or Pinyon Mtn Road, it would have been a long walk-out in the heat. I am assuming it was in the section north of Whale Peak (the road is at an altitude of about 2600 feet - there's a ridge to cross to get to Harper Flat). If people have enough water to wait until dark, then the obvious thing to do is take your flashlight and use the road to walk to the 52 - it's a relatively wide and flat dirt road, not a cross-country hike into a canyon. Meanwhile, stay in the shade of the truck itself. Soak your hat in water and attempt not to move much. It could have been as hot as 120F in Harper Canyon at 3-4 pm. It likely would have been about 110-112 in the shade at 3 pm up on Pinyon Mtn Road. I think it's telling that LE has mentioned a lack of evidence of water. I assume that means neither person had a camelpak style water carrier in evidence. I was struck all along (esp in the picture at Thermal) at the lack of a big water supply in the back of the truck.
Surely they thought they were just doing a day trip when something went wrong. They could have been camping somewhere off Pinyon Mtn Road, as well (dispersed camping) and their things might never be found or identified, after mid-August.
IMO.