Evidence of the great westward migration remains in these shallow depressions, once deep ruts made by thousands of hooves, shoes, and wheels. Although the Overland Trail is often imagined as a single well-defined road, the actual route through the Platte Valley in any given year varied considerably except in narrow places such as this, depending on soil conditions and the availability of grass for animals. Emigrants traveled an average of fifteen to twenty miles a day in various conveyances and spent four to six months on the long journey from the Missouri River to Oregon or California. Even at its best the trip was arduous and often marked by the dusty monotony of daily routine. At other times, disease and Indian attacks posed very real dangers, and the many fresh graves along the road testified to the sacrifices of many pioneers. Some emigrants were better equipped, some were wiser, and some were simply luckier, but all endured weariness, hardship, and danger. As many overland diaries and letters show, this was a great human experience and one vital to the settlement of the West.