During the great western migration to California in the late 1840s and 1850s, neither excited gold-seekers, nor families simply wanting to settle, could depart overland for the Pacific Coast at just any time they wished. Theirs was a limited window of travel time, framed by potential hazards at both ends of the route. Since their sole means of transportation was draft animals, they had to wait for spring grasses to sprout on the prairies, as fodder for their wagon-hauling oxen and other livestock. Normally, this was the month of April or early May. Their destination deadline was to safely cross the formidable Sierra Nevada before the winter snowfall, which might begin at the end of October. They had, in effect, six months or less to cross 2,000 miles from the Missouri River to the Sacramento Valley. It was imperative that their wagon trains moved along at a brisk pace, at least six days a week from sunrise to sunset (with a mandatory stop at lunch to rest and feed the animals), to allow for intentional layovers and the inevitable slowing at river crossings. Average travel distance on flat plains was 14-20 miles a day, reduced to 3 or 4 miles (or less) per day through difficult terrain. Once the going got rough, only very small children and the desperately sick rode inside the covered wagons. Adults and youngsters walked the trails to spare their animals from the burden of unnecessary weight.