On Saturday July 30 2016 I took a solo scouting hike up Indian Truck Trail from the Corona side of the Santa Ana Mountains; this is a great trail, though long.
Indian Truck Trail is a maintained fire road that's about 7 miles from trailhead to Main Divide, and it's bracketed by Mayhew Canyon to the north and Indian Canyon to the south. Like most driveable roads, it's not a ridgeline trail that hugs the top of the topography. Instead the road has cuts into the mountain when necessary to maintain a steady but not steep incline.
The road itself is wide and relatively smooth, and it's used by service vehicles headed to Santiago Peak to take care of all the radio gear up there. A high-clearance vehicle would have no trouble at all, and even my low-clearance Dodge Charger could make most (but not all) of the trip. It's a much better surface than Trabuco Creek Road, which provides access to the Holy Jim trailhead. I saw numerous Jeeps, mountain bikers, and dirt bikers enjoying the trail.

Image from Bing Streetside
Knowing this would be a long hike, I actually drove up a ways from the trailhead, which is in a new residential area, to park along the side of the road before setting off. I had planned on using a large parking lot of a religious retreat center tucked up in the mountains, but it had a clear "Private Property" sign, so I decided against trespass. Though I backtracked to park, in restrospect I could have gone farther up; for a single car there were plenty of places to park along the side of the road. For any kind of group outing, I'd approach the retreat center asking for permission.
It was slated to be a hot day so I got a very early start, arriving at the trailhead right at 7AM. Though it wasn't hot yet, I could feel that it was coming. It was totally worth getting up at 5AM to get this kind of early start.
I had 10 liters (22 pounds) of water with me: 3L in my Osprey hydration bladder, plus 7L in individual Playtpus SoftBottles. All of it was ice cold—including two liters fully frozen—and very welcome. I ended up using all the water.
The trip up was quite pleasant: no really steep spots, enough regular shade, either from trees or from the mountain cuts blocking the sun, to really take the edge off if I needed to stop and rest. The trees, especially beautiful pines, increased on the way up, and it was just a pretty hike the whole way.
My primary goal had been just to reach Main Divide, but if I felt good I'd press on and cover more. I felt great, so I did, heading north for a mile and a half to rest at Bear Spring.
Everybody who's done Santiago Peak via Holy Jim has been through Bear Spring: this is where the Lower Holy Jim Trail reaches Main Divide Road, and it's as nice a rest stop as you can find in the Santa Ana Mountains. A large area under canopy, with places to sit and relax, it's a natural and obvious stopping point, and I took probably 20 minutes to refill they hydratino pack from the individual 1L bottles, have some lunch, and just take a load off. I was happy to wave to cyclists and dirt bikers and Jeepsters heading by.

Refreshed, I headed back, noting the Upper Holy Jim Trailhead about 1/3 mile east of Bear Spring on my way back to the Indian Truck Trail junction. This sign is really easy to miss if you're not looking for it.
Reaching the junction I still felt pretty good, so decided to press on along Main Divide to the base of Trabuco Peak. I had hit the top of the peak on a previous trip, but from the south - I had not yet done this segment of Main Divide. Having it incorrectly in my head that it was just a mile, I headed off. It was difficult almost immediately.
This portion felt quite a bit steeper than the rest, though in retrospect it probably wasn't: it just felt like it. I had already hiked more than 9 miles with around 2500' of elevation gain, in temperatures that had to be approaching 100F, so I was just wiped out. And realizing that it's a two-mile trip, not one, was very discouraging: multiple times I really thought about heading back.
At one point I found a great shady spot where the side of the road had been reinforced with concrete, so it formed a kind of long bench, and this was a great spot to stop and recharge. Refilled my hydration pack - which still had ice! - had a snack, and just took it easy. Not as nice as Bear Spring, but this was really the key to reinvorate me to continue. It was really, really hot.
Reaching the base of Trabuco Peak, where there's a small sign marking the location, I was very happy to mark a GPS waypoint and turn around. The trip back was much nicer (downhill!). And as is my habit on all hikes, I rolled my ankle pretty painfully, but thankfully it wasn't serious and I was able to continue.
At this point I started to feel a blister forming on my left heel, something I've not had in a long time. I wear great wool socks from Darn Tough, but I guess the distance was getting the better of me. I waited until I reached the junction with Indian Truck Trail, with good shade, to put on a blister bandage for the trip down.
I also refilled my hydration bladder for the last time; I now had 3L of mostly-cold water in the bladder, with just 1L in a Platypus bottle for reserve. Four liters of water is a little on the low side for a >6 mile trek on a crazy hot day, but the trip was all downhill and I had been hydrading really well all day.
The trip down was uneventful, but still very hot, but thankfully with shade here and there. The blister bothered me some all the way down, but not badly, I made pretty good time all the way down, though I was sorely tempted to hitch a ride with the several trucks headed down. If I had actually run out of water or had been simply unable to continue, I would have, but I am thankful I decided to tough it out.

As I approached my car, I was able to use the awesome feature of remote-start, so 200 yards away started the car and got the A/C cranking. Upon reaching the the car, I marked the end of the hike in my GPS, doffed all my hiking gear, and changed my shirt (I always keep a fresh post-hike shirt in the trunk).
Getting in the car and enjoying the A/C, I reached for my cooler. I had stopped at a Von's grocery store on the way, filling the cooler with a bag of ice and three quart-bottles of Gatorade on the off chance that I'd be thirsty when I got down. Duh :-) All three were gone before I reached home an hour later.
This trail has pretty much all the hallmarks of a great hike: reasonable parking access, a good rally point for meeting (the grocery store plaza), an enjoyable non-steep trail, with only the distance being a possible negative: I figured about 16 miles if we have permission to use the retreat's parking lot, maybe a bit less if I can find a closer spot on the side of the road.
The Map
This map shows a bit more detail of the trail. Starting in the upper right, the blue arrows show the direction of travel, and blue numbers show the elevation as taken from the USGS topo maps.
I also included the full Holy Jim trail (including parking spot) to give a point of reference to those who've done this trail to Santiago Peak before. The peak was visible for much of the second half of the hike, though obviously much higher.

click for larger image
Total distance via my walkmeter (iPhone app) was 19.73 miles, though more accurate GPS distance is more like 19.25. Total time, including breaks, was 8 hours 45 minutes. A great trail, but not on such a hot day.