Several explorers are notable for their exploration of the Rocky Mountains and Colorado:

• The Vérendrye brothers, French trappers and hunters, were possibly the first Europeans to cross the northern Great Plains and see the Rocky Mountains during an expedition in 1742–1743

• Spanish explorers were among the earliest Europeans to enter the region. Francisco Vázquez de Coronado led an expedition into the Rocky Mountain region from the south in 1540

. Other Spanish expeditions, such as those led by Juan de Archuleta (mid-1500s) and Juan de Ulibarri (1706), also penetrated parts of Colorado

• French fur traders Pierre and Paul Mallet discovered the Rocky Mountains' headwaters of the Platte River in 1739, becoming the first Europeans to report on the mountain range

• Sir Alexander Mackenzie was the first European to cross the Rocky Mountains in 1793, reaching the Pacific coast in what is now Canada

• The Lewis and Clark Expedition (1804–1806) conducted the first scientific reconnaissance of the Rockies, paving the way for further exploration from the East

• John Charles Frémont, an American explorer and cartographer, crossed Colorado on various expeditions in the 1840s and 1850s

• John Williams Gunnison, a US Army officer, explored the Western Slope of Colorado in 1853 while searching for a railroad route across the Rockies

• Mountain men and trappers such as Jedediah Smith, Jim Bridger, Jim Beckwourth, Hugh Glass, and Joe Meek were also significant early explorers of the Rocky Mountains

In summary, exploration of the Rocky Mountains and Colorado involved Spanish expeditions in the 1500s and 1700s, French fur traders and trappers in the 1700s, and American explorers such as Lewis and Clark, Frémont, and Gunnison in the 1800s