Not until 1827 did the Sierra first succumb to a crossing by the new people, and then it was not the Spaniards who finally accomplished the feat, but a new breed of naturalized Europeans emanating from the upstart republic of the United States of America. These men were motivated not by the large goals of empire or salvation, as the Spaniards had been, but by an ambition for personal advantage, and a rather considerable dose of sheer curiosity. During the 1820s the rapid harvesting of the beaver of the Rocky Mountains had sent adventuresome trappers farther and farther afield in search of un-trapped beaver habitat. It was only a matter of time before the trappers of the Rockies found their way into contact with the Mexican settlements of Upper California. (Mexico had separated from Spain in 1821 and taken California with it.) Already contact between the two cultures had been made in New Mexico. Nevertheless, California authorities were not pleased when trapper Jedediah Smith succeeded in crossing the Great Basin and finding his way to Mission San Gabriel in late 1826. Mexican Governor Echeandia ordered Smith out of California, but during the winter and spring of 1827 Smith instead wandered north through the San Joaquin Valley, trapping the numerous beaver of the valley's rivers and noting the lay of the country. His first attempt to cross the Sierra took him up the Kings River, where the extremely rugged terrain and the earliness of the season stopped him cold. Finally, in May, on his second try, Smith succeeded in crossing the mountains in the vicinity of the Stanislaus River, east of modern Stockton. Smith returned to trap in the San Joaquin in 1828, and in 1829 and 1830 employees of the Hudson's Bay Company trapped the same areas. As knowledge of California spread, the number of trappers increased. [2]

In 1832-33 a party that included Ewing Young and J. J. Warner trapped the Kings River "some distance into the mountains." [3] During 1833 and 1834, a party led by Joseph Reddeford Walker crossed the Sierra from the east in the Yosemite country, and proceeded south along the western foothills of the Sierra. Finally, taking the advice of local Indians, they departed through the Kern River route still known as Walker Pass. Once across the Sierra a second time, Walker turned north and explored the Owens Valley country, taking a hard look at the severe eastern face of the Sierra. Finally he connected with his route of the previous year and turned east. [4]

It did not take long to exhaust the beaver populations of the Sierra foothills. Unlike the Rockies, the Sierra had beaver only at the lowest altitudes. California beaver depended mostly upon cottonwood trees for their sustenance, and since significant cottonwood groves were limited to foothill and valley riverbanks, the fur trappers had little cause to explore the high country in any detail. But in late 1844, Second Lieutenant John C. Fremont of the U. S. Topographical Engineers, illegally exploring the fringes of Mexican California for the U. S. Army on the eve of the Mexican War, made a serious attempt to cross the high country of the southern Sierra. It was late December, and Fremont's goal was to rendezvous with the remainder of his party on the east side of the mountains. He left Sutter's Fort (modern Sacramento) on December 14 and ascended the Kings River, following the north bank. As the canyon narrowed, Fremont climbed out of the canyon and followed the ridges to the northeast. Finally, having climbed all the way to timberline, he found himself not on the crest of the Sierra but somewhere on the divide between the North Fork of the Kings and the South Fork of the San Joaquin River. To the east rose masses of 13,000-foot peaks. That night a snowstorm began, and by morning the explorer abandoned all further thought of crossing the Sierra. Only with difficulty did Fremont and his party succeed in regaining the floor of the San Joaquin Valley. Had they been another day or two's travel into the mountains, they might not have escaped at all. [5]

Smith, Walker, Fremont and their contemporaries established the basic truths about the southern Sierra. Along the western slope deep, rugged canyons made travel very difficult. To the east, the high peaks of the crest stood as a barrier visible for a hundred miles. Between was a barren difficult land of high peaks and nearly impassible gorges. If one wanted to get to the other side of the southern Sierra, it was best to go around.