In the late 1700s, several Spanish expeditions set out from New Mexico to establish trade routes across the Great Basin to California. However, there is no evidence that any of these parties reached the east side of the Sierra Nevada until the early 1800s. In an 1806, Gabriel Moraga, a Mexican-born officer in the Spanish army with a company of 15 men, made the first documented entry by non-natives into the Sierra Nevada.
In the 1820s, Euro-American explorers and fur trappers began looking for ways to cross over the Sierra into what was then Mexican California. In 1827, Jedediah Smith, with two men and enough horses to carry more than 1,500 pounds of beaver pelts, became the first non-native party to traverse the range from west to east, which they did near Ebbetts Pass, about 80 miles north of Devils Postpile.
Traveling from the Great Salt Lake, Joseph Walker crossed the Sierra from east to west with 70 men in 1833, becoming probably the first non-natives to see the Yosemite Valley. They struggled through the maze of granite gorges north of the Tuolumne River where they encountered impassable cliffs and deep snowdrifts. Running low on food, they had to butcher some of their horses. They happened upon the Mono trail, which was the main Indian route from Mono Lake across Tuolumne Meadows to the western foothills. Based on the advice of Indians on the west slope, they returned by a far easier route 180 miles to the south, over what would later be named Walker Pass.
In the mid-1840s, John Frémont led expeditions to survey the western and eastern ﬂanks of the Sierra and mapped many of the easiest passages through the mountains. Fear of conflicts with Indians deterred Euro-American settlers from entering the Sierra Nevada, but after Mexico ceded California to the United States along with most of the current US Southwest, the increased presence of the US military emboldened settlement there. Miners, loggers, and sheepherders began to arrive, especially after the discovery of gold in the Sierra Nevada in 1848. However, the highest elevations of the Central Sierra and the less commonly used Indian routes, including the Mammoth Pass trail east of Devils Postpile, remained unexplored by Euro-Americans until the late 1800s.