After seeing margotr's photos from a recent full descent of the Little Colorado River (LCR) Gorge, I had to see this place myself, even if I have to do it in several shorter segments. This trip report covers Horse Trail to the LCR, downstream past Blue Springs and exiting up Salt Trail Canyon (approximately 16.5 miles, 3000' elevation).
Horse Trail is easy to find and the route down is straightforward, except for some back and forth traversing to drop through the final cliff bands just above the river. Even though the USGS gage for the LCR at Cameron had been reading nearly zero for a couple of weeks and the river looked dry from the Cameron bridge, there was a small flow of fairly clear water down in the gorge from springs located a couple miles upstream. After heading downstream for several miles of gentle, pleasant walking, many more small springs appear at the sides of the gorge, gradually adding to the flow and the faint blue color. Some are surface flows, some bubble up through the sand, others look to be old springs that are no longer active. Soon you arrive at the much larger Blue Springs, surging up powerfully from below a limestone cliff, wonderfully warm and flowing out so strong that I couldn't swim against the current. What an amazing place.
I would say that Horse Trail is definitely the easiest way to get to the springs. Attempts from the west side are possible but require a brutal drive and then dangerous (borderline insane) scrambling to find a route down the cliffs. I know of more than one party who failed to reach the springs from there. In contrast, the start of Horse Trail is an easy drive on good roads from Highway 89 on the Navajo reservation (best to get a Navajo permit at the 89/64 junction in Cameron, they're only open on weekdays in the winter). The Horse Trail is about 2 miles in length and a 1700' drop to the LCR. From there, Blue Springs is an easy 5 miles downstream.
You could return back the way you came, but about 6.5 miles further downstream from Blue Springs is the bottom of the Salt Trail Canyon exit. This stretch has a stronger current and more vegetation to deal with (additional springs keep adding to the flow, multiple crossings and possible swims (drybag) required), but this takes you through the heart of this incredible river. Just make sure it will be flowing that indescribable electric blue color (instead of brown) when you go. From the top of Salt Canyon, the shuttle back to the Horse Trail start is 30 miles (a nice mountain bike ride if you do it the day before).