After gold was discovered in 1848, California became the main destination, and after 1849 many emigrants and gold seekers traveled the trail on the north side of the Platte. During the peak migration years, the route to Oregon or California was not a single clearly defined pathway but varied with weather and destination. Historian Merrill Mattes estimated that as many as 500,000 people went west on various branches of the Great Platte River Road between 1841 and 1866. Beginning in the early 1840s, thousands crossed the continent to settle in the Oregon country, following the south bank of the Platte and North Platte Rivers on the way to South Pass in the Rockies. Emigrants often described the Platte as a mile wide and inches deep, treacherous to ford, and too muddy to drink.