I have wandered that general area and been on short sections of the trail. I really doubt you’d find any homeless people on that route even in the suburban/urban areas. In the more backcountry areas, it is far too hot to live there.
The route starts at Torrey Pines and runs to Carmel Valley. Those are very expensive areas to live in. You’re more likely to be yelled at by rich people. The area around El Cajon will be pretty deserted and the ascent up to the mountain is ridiculously brushy. The brush in SoCal is covered with thorns. Even the soft-looking plants are thorny. I wound consider gaiters.
Cuyamaca Rancho park is also near a very wealthy area along the lake. It’s a really neat and infrequently traveled area. If you have time, a visit to Stonewall Peak is worth it. At certain angles, it looks like class IV, but it’s really class II.
I can see a few problems:
1) Heat: don’t take this lightly. It can get really hot. As in, they close down El Cajon mountain due to too many rescues during parts of the year. If you go in the warmer season, bring an umbrella and gatorade.
2) Rain: if the spring, it can rain. It can get cold. It can get windy. I nearly got hypothermia once in the desert. I had a jacket but no rain pants or rain shells for my hands. I was so could that I couldn’t unzip my jacket. I would bring full body rain gear: jacket, rain pants, rain mitts. Also, an umbrella.
3) Water: Unless you’re in a park, I wouldn’t rely on water sources. “Year-round” water sources often don’t exist year-round.
4) Route finding: good idea on trying to get a GPS track. There are so many washes and canyons that it’s so easy to get lost and go up the wrong canyon 50 feet away. That being said, GPS is probably not enough. At times, you’re probably going to want USGS maps and a fair amount of skill to interpret them with a compass. Since there’s no tree coverage, you can always scramble up to a high point and get your bearings, but often there’s no obvious route up. Budget extra time for this. You can waste hours wandering around trying to figure out where you are.
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