Smith spent the winter absorbing details of the Hudson's Bay Company trapping operation. He then went to Henry's Fork and, in June 1825, became William Ashley's new partner, replacing Andrew Henry, who had decided to leave the fur trade. They carried a large number of furs to a rendezvous with traders who took the furs back to St. Louis. After another such rendezvous the following year, Ashley sold his interest in the organization to Smith, David E. Jackson, and William Sublette.

In August 1826, the three new partners divided their efforts in order to go on the fall fur hunt. Smith and a group of 16 men went south, to the Great Salt Lake area. They followed the Virgin River to where it met the Colorado River, then continued south to a group of Mojave villages near what is now Needles, Calif. They survived a brutal two-week journey across the Mojave Desert and reached the San Gabriel Mission, near what is now Los Angeles.

Smith had caught the attention of Spain's governor, José María Echeandía, who called him to San Diego for questioning. After convincing the governor that he was on nothing but a business expedition and promising not to return to California, Smith returned to the edge of the Mojave Desert but then went north, through the San Joaquin Valley to the edge of the Sierra Nevada. Smith and two companies then left the company for a planned rendezvous on Bear Lake. They went to the source of the Stanislaus River and then crossed the Sierra Nevada through Ebbett's Pass. One of his companions, Robert Evans, died while crossing the subsequent Great Salt Desert. Smith and the other survivor, Silas Gobel, carried on and reached the rendezvous point on Bear Lake on July 3, 1827.

Smith's next trip was back to California and back to the Mojave villages he had visited before. The reception this time was not as friendly. A Mojave war party attacked Smith's group, in response to what Smith later learned was an attacker on them by other trappers the previous winter, and Smith a handful of others survived. Smith again faced an audience with the Spanish governor and again avoided being arrested or executed. He again went north, to what is now Red Bluff, Calif. They continued on, through the Willamette Valley, reaching Fort Vancouver with a much reduced force after an attack by Kelawatset Native Americans along the way, in what was called the Umpqua Massacre. Smith and an armed party returned to the site of the massacre but found no trace of the attackers.

Smith wintered at Fort Vancouver and then set out east, in 1829. After that year's rendezvous and one other, Smith and his partners decided to sell their interests in the fur trading company. The new buyers included Jim Bridger, with whom he had trapped for a time, and Thomas Fitzpatrick, who formed the Rocky Mountain Fur Company. Smith headed further east, reaching St. Louis on Oct. 7, 1830 and settled down to some peaceful time, writing journals and perfecting maps that he had drawn of his travels. He did not complete this work.

Smith grew restless after a time and decided to rejoin the fur trade, this time focusing on the southwest. He joined a wagon train headed for Santa Fe in April 1831. The party ran out of water in what is now Kansas, on the Cimarron cutoff of the Santa Fe Trail, near what is today Ulysses. Smith set out to find water and found a Comanche war party as well. He died on May 27. He was 32.

Smith could claim many firsts:

• He was the first American to lead a party cross the Sierra Nevada.
• He and his men were the first to enter California from the east, surviving a harrowing journey across the forbidding Mojave Desert.
• He was also the first leader of a party to return from California overland.
• He was the first American to lead a party overland up the California coast to Oregon.