Shortly after James W. Marshall discovered gold at Sutter's Mill, his Mormon laborers were recalled to the Great Salt Lake Valley in Utah. On April 9, 1848, a plan was devised to cut a wagon trail through the uncharted Sierra Nevada frontier, and that trail became the present-day Mormon Emigrant Trail. In June, the wagon train departed Pleasant Valley with 45 men, one woman, 17 wagons, several yoke of oxen, and 300 head of cattle. Their first campsite was made on July 4, 1848, by Mormon scout Jason Calvin Sly at today's Sly Park. From there the wagon road was cut inch by inch through the austere Sierra mountain range. When completed, the Mormons had built the first east-west wagon road into Northern California, and tens of thousands used it during California's gold rush for commerce and stagecoach travel.