Exploration
Pike left Fort Bellefontaine near St. Louis, Missouri on July 15 with a detachment of 20 soldiers and the 50 freed prisoners. They followed the Missouri and Osage rivers to the Osage village at the present-day border of Kansas and Missouri. There, they returned the hostages and parleyed with the natives. Striking northwest, the group made for the Pawnee territory on the Republican River in southern Nebraska. At the Pawnee village on September 29, Pike met with the Pawnee council and announced the new protectorship of the United States government over the territory. He instructed them to remove a Spanish flag and to fly the Stars and Stripes instead.
The expeditionary force then turned south and struck out across the prairie for the Arkansas River. They reached the river on October 14, and the party split in two. One group, under Lieutenant James Biddle Wilkinson, travelled downstream along the length of the Arkansas to its mouth and back up the Mississippi to St. Louis. Pike lead the other group upstream, to the west, toward the headwaters.
Disappointed in the landscape, in his memoirs Pike called the prairie he had crossed The Great American Desert -- a term that stuck, and discouraged settlement for decades.
On November 15 Pike first saw the shadowy distant mountain he called "Grand Peak", which has since been known as Pikes Peak. Pike made an attempt to climb the peak, but was unequipped to achieve the 14,000-foot summit. Despite the coming winter, Pike pressed forwards up the Arkansas, and on December 7 the party reached Royal Gorge, a spectacular canyon on the Arkansas at the base of the Rocky Mountains.
The party's next goal was to reach the headwaters of the Red River and head back downstream to the Mississippi and relative safety. However, the company's bearings were at this point far askew, and they made several blundering steps in an attempt to find the river. In addition, they were not equipped for a mountain expedition, nor for hard winter weather. Heading north, the party found the South Fork of the Platte River, and following it upstream came to what they thought was the headwaters of the Red. Turning back downstream, they returned to the point at which they had left the Arkansas originally. In fact, they had executed a large, weeks-long loop.
Hungry, cold, and exhausted, the party headed south over the mountains. Several men were left behind as they dropped from exhaustion, but Pike doggedly pressed on until January 30, when he came to the Rio Grande at a point near Alamosa, Colorado. Pike mistook the Rio Grande for the Red River he had been seeking. Here, he built a fort and attempted to regroup his men, strewn across miles of mountains behind him.
Capture
At this fort on February 26 Pike and his remaining men were captured by Spanish soldiers from nearby Santa Fe. Arresting the party as spies -- which, in a way, they were -- the Spanish collected the rest of his men that remained unrescued and marched them south. The prisoners were marched through Santa Fe, Albuquerque, and El Paso to Chihuahua, the state capital. Along the way, Pike's party was treated with respect and celebrated by the Mexican locals, and Pike made careful notes of the military strength and civilian population.
Chihuahua's Governor Salcedo was unable to keep a military officer of a neighboring country, still keeping up the pretense of friendliness, incarcerated for long. He ordered the repatriation of Pike, although some of his party were kept in jail in Mexico for years.
Pike and some of his party were escorted north, through San Antonio, Texas, arriving at the border with Louisiana at Natchitoches on July 1, 1807. The Spanish formally complained to the United States Department of State, but the government maintained that the party had been one of exploration only. Ironically, Pike's capture by the Spanish, and consequent travels through New Mexico, northern Mexico, and Texas gave him more information about Spanish power than his exploration could ever have done.
Aftermath
In many ways, the expedition was less than successful. Pike's abilities as a naturalist and ethnographer were nowhere near the level of his compatriots Meriwether Lewis and William Clark. His notes had been confiscated by the Spanish, so when he eventually published his memoirs in 1810, they were composed from memory and thus vague and factually inaccurate. Pike had not been able to make contact with as many Native American nations as he had hoped, nor to convince them to submit to United States authority. He was unable to traverse the Red River.
However, the party had travelled more of the western Great Plains than any previous American, and they had made important discoveries in the Rocky Mountains. Their path across the west would form the kernel of the Santa Fe Trail, used by thousands of American pioneers.