The Bonneville Salt Flats were formed as ancient Lake Bonneville slowly evaporated and deposited concentrations of salt onto this playa, with shorelines carved into the mountainsides still visible to the north along the Silver Island range and extending to the Salt Lake Valley. Named after Captain B.L. Bonneville, an early military explorer of the West, the salt flats measure over 44,000 acres and are primarily public lands. Historically, the flats impeded westward movement, and early traders such as Jedediah Smith and John Fremont crossed the vast saline plains and returned with stories of the salt's harshness. In 1846, the Donner Reed party lost animals, wagons, and valuable time on the salt, losses that contributed to their late arrival and subsequent disaster in the snowy Sierra-Nevada Mountains. The flats' potential for racing was first recognized in 1896 by W.D. Rishel, who attempted to organize a carriage and bike race, and he convinced Ferg Johnson to test drive his Packard here in 1911. In 1914, Teddy Tetzlaff reached 141 mph in his Blitzen Benz, and in succeeding years many tried to set faster records. In 1940, Ab Jenkins set 81 new speed records in his Mormon Meteor III, including a 24-hour endurance record of 161 mph. In the 1960s, jet and rocket cars appeared and exceeded the 500 and 600 mph marks. The speedway, 80 feet wide and 10 miles long, is prepared by the Bureau of Land Management in early summer, with speed trials scheduled through summer and fall until rains cover the area with water.