Oregon Trail wagons were kept small because large, heavy wagons could not make it over the mountains. People rode in the back only if they were sick or tired, but most of the time they walked beside the wagon, with the men leading the oxen. Oxen were preferred over horses or mules because they were cheaper, could pull heavy loads, did not bog down in the mud, and did not stampede. Depending on the terrain, travelers could cover from 5 to 25 miles in a day, and it took four months to reach this area from Missouri. These wagons were not Conestoga wagons, which were larger, heavier vehicles used in the East and on flatter trails such as the Santa Fe.