Above the Arkansas River, which formed an international boundary between the United States and Mexico during the early years of the Santa Fe Trail, wagon traffic crossed flood-prone ground by hauling onto higher bluffs to avoid the wet bottomlands and make the easiest passage through the terrain. The trail split a few miles west, where traders chose either the Mountain Route or the Cimarron Route, which led by multiple river crossings into Mexico. As more wagons passed, the ruts grew deeper, and wagons traveling abreast left parallel tracks across the prairie. Rebecca Mayer wrote in 1852 of reaching the Cimarron, where everything looked lush and green but there was not a tree or a bush, and where the river was nothing more than a dirty pool of stagnant water. Fort Dodge, shown about 1867, protected travelers on the trail.