Did he say he was going through Utah? If he doesn’t turn left by Amarillo, if he continues north from there, he’ll have to cross the Rocky Mtns to get to Utah. At least some passages on the highways & roadways won’t be entirely passable for a horse, I don’t think.
But the point is a good one. Should he route through Utah or through Colorado, as he gets into the northern parts of either of those states, he is going to start running into a lot of public lands. And very large National Parks.