Railroader's Dream Hike!
This is a really fun hike to a very interesting destination: the Trestle over Goat Canyon, or Carrizo Gorge. There is a lot of history surrounding this trestle, but I won't deal with that here, this is strictly for the hike. Ample resources exist on the internet to learn about the trestle, the railroad, and their construction, but this write-up is for the hike.
It is my opinion that this has always been a social trail hike, and it is gaining popularity, so route finding should improve, despite the lack of real trail construction. Due to this hike's destination, it may attract those who don't normally hike in wild areas. Know that there is no reliable water out here, no cell reception, and you are very likely to be totally alone, all day. I do not know if people come more by the tracks or the trail, but a notebook located near the tunnel entrance at the far end of the trestle filled up in 2016, so this is still a fairly popular destination.
Access to the Mortero Palm Canyon Trailhead is a decent challenge. I was able to do it just fine in my 2013 Subaru Outback, knowing where to start from off of the S2 highway. In fact, I basically just went with the dominant 2-track once I left the S2. This is an important idea, as a similar concept can be employed to hike this well worn social trail hike.
From the trailhead, which is basically a turn around at a dead end, walk down into the wash and down wash slightly, locating a beaten path that appears in the riparian vegetation. From here, follow the trail to the next canyon to the north. This next canyon is the one with the Mortero Palms. These palms are visible from the road as you drive in and are still a few miles out, but not on any part of the hike.
At times, this hike has a lot of braided social trails, but at other it is a clear trail, almost built in some spots. Down low, it is often braided. You want to follow the best trail, or the one that takes you to a (probably) dry stock tank. At this point you have two options, one I recommend (option 1), and one I do not (option 2). For option 1, I recommend turning north and following a trail running parallel off the long side of the tank. This is a social trail that gets better once through the low vegetation, is generally visible and cairned for it's length. Going perpendicular to the long side of the tank and continuing up canyon to the palms is option 2. If you only came for the palms, take option 2.
I took option 1 because I went out with the logical idea that the best route, or the one most visible to me while going out, goes to the palms and then on. In reality, my experience was that the best route goes to the trestle and does not go through the palms. So, option 1 leaves the tank and crosses into the next drainage or slope to the north. It is well traveled and cairned as it climbs steeply up on to a ridge before it tops out and drops down into the upper parts of Mortero Canyon. Though this social trail is steep, sometimes loose, and gains a couple of hundred more feet in elevation than if one stayed in Mortero Canyon, you never have to get around or over large granite boulders or put yourself in situations where a fall may be deadly. I felt this way, at least.
After cresting the ridge, the trail is very defined and loses some elevation as it drops back to upper Mortero Canyon. From this point, I do not recall a lot of braiding or confusing side trails. It is a pretty straight forward hike across rolling terrain to upper Goat Canyon. Enjoy the scenery, the views to the east when they are there, and look for sheep. I wasn't even trying when I spotted to Ewes on the ridge above. Well, I saw 1, there were 2 in the picture.
Descending to Goat Canyon starts easy enough, and has only small areas of boulders to get around. This is once again cairned for route finding. The situation changes as you get further down and the canyon steepens. Remember that this is a pretty popular route, so it should be doable. Some parts do constitute technical hiking or scrambling, but not climbing, in my opinion. Early on there are no views of the railroad, then distant views of the tracks come in to view. Eventually, once pretty far down canyon and nearly to the trestle, you catch your first glimpse of it. Confirmation that you are on the correct path to some destination, after all! The final descent is steep and may be challenging, but it is marked by cairns and slow travel with the idea that someone else came before you should keep you on safe terrain. Once into the boulders, things begin to let up, you soon level out, and then you pretty much just walk over to the railroad.
At present, it is not recommended to return via the railroad, as that is appearantly illegal, despite being owned by the City of Sand Diego (from what I found on March 16, 2017). With the current rock falls over the railroad near the trestle, no trains will be coming through any time soon. Hike around the nearby tunnels, over the trestle, maybe go down canyon and explore what appeared to be water flowing in Goat Canyon after the wet winter of 2017, and then return the way you came. If you are backpacking, you probably want to stay nearby.
More on Option 2.
Keeping in mind that I recommend option 1, some may take option 2. I went out on option 1, but knowingly broke my rule of returning the way I came and descended through option 2, simply because I wanted to see the Mortero Palms. I knew it was a route, after all there were ample foot prints in the gravel on the bottom of the wash, but I could have gotten into trouble. This is because above the palms, a few sections of the route were very hard for me to locate, or I just got completely off route in the rapidly waning daylight, and I ended up scrambling down some rather large boulders. Being alone, a fall here would have been deadly. It could simply be that I didn't pay attention and was way off route, but I greatly preferred the trail conditions of option 1. If you still want to see the palms, it is probably better to head to them, visit the main groves, and then return to option 1, either before or after your primary hike to the trestle.
WARNING! Hiking and outdoor related sports can be dangerous. Be responsible and prepare for the trip. Study the area you are entering and plan accordingly. Dress for the current and unexpected weather changes. Take plenty of water. Never go alone. Make an itinerary with your plan(s), route(s), destination(s) and expected return time. Give your itinerary to trusted family and/or friends.