So we'd head down the trail, and the lead horse would be on high alert (ears forward, body tensed up) and might even start trying to turn around back the way we'd come. So we'd pull the other one into lead position to coerce the other down the trail a little further, and then at one point both horses refused to go any further. Neither Julie nor I are the bravest horsepeople, and it is entirely possible that they were spooking because of something totally harmless, or even just to convince us to head back to the trailer. But we decided to play it safe and assume the horses knew better than we did, so we turned around.
When we got back to a junction, we explored a different direction for a bit, and again the horses refused to go forward after a certain point, so we called it a day and headed back.
On our final pass by the supposedly horse-eating signs, I circled the horse back around them at what she felt was a safe distance but with much protesting. Then I got her to get a little closer, but again with much protesting. Then all of a sudden, she just walked right up to the signs, as if to convince me that they were okay after all. Then spooked again walking away and a few times again even though we were heading TOWARD the trail. But again, her form of spooking is totally doable, even by me, so whatever.
We eventually ended up back at the trailer, where the horses loaded up very nicely, and we all headed back toward food, water, and shade.