Twenty-three days into the journey, as the party was exploring near Yellowstone Lake, the nearsighted Everts went missing. However, this had not been an uncommon occurrence for Truman, who, according to diaries from the expedition, had already been separated multiple times. At first, Everts was unconcerned by this separation, writing that “As separations like this had frequently occurred. It gave me no alarm, and I rode on, fully confident of soon rejoining the company, or of finding their camp… I rode on in the direction I supposed had been taken until darkness overtook me in the dense forest. I selected a spot for comfortable repose, picketed my horse, built a fire, and went to sleep.” Nathaniel P. Langford, one of the trips leaders was similarly unconcerned, as he wrote in his journal that “One of our comrades (the Hon. Truman C. Everts, late U.S. Assessor of Montana) had failed to come up with the rest of the company; but as this was a common circumstance, we gave it little heed until the lateness of the hour convinced us he had lost his way. We increased our fire and fired our guns, as signals; but all to no purpose.” But the expectation of both men did not come to pass. This time, the Hon. Truman C. Everts stayed very much lost.
The next day, Everts awoke. Convinced he would be able to rejoin his party on the beach of Yellowstone Lake, he recommenced his search. However, it didn’t take long for the accident-prone Everts to commit his first grave mistake, which would ultimately be a custom of his in the horrible series of misadventures to come. When he hopped off his horse to better navigate a challenging section of terrain, he neglected to harness it. Much to his dismay, the untethered horse promptly bolted away into the vast wilderness, carrying with it the vast majority of the supplies Everts would need to survive. “I turned around just in time to see him disappearing at full speed among the trees… My blankets, gun, pistols, fishing tackle, matches—everything, except the clothing on my person, a couple of knives, and a small opera-glass were attached to the saddle.” In an act of futility, he spent the first half of the next day searching for his astray horse, posting notes to his comrades along the way in the hopes they would discover them.
Finally, without his provisions, and with the emerging realization that he would be spending yet another night alone in the wilderness, the full gravity of this situation was becoming apparent to him. “I realized I was lost. Then came a crushing sense of destitution. No food, no fire; no means to procure either; alone in an unexplored wilderness, one hundred and fifty miles from the nearest human abode, surrounded by wild beasts, and famishing with hunger. It was no time for despondency.” Meanwhile, search parties from the expedition frantically combed the wilderness for the lost Everts. For days they battled the harsh elements of Yellowstone in hopes of rescuing him but to no avail. One search party came incredibly close to reaching Everts as he was laying near the shore of Heart Lake, huddled around nearby some thermal features in an attempt to stay warm. However, they were forced to turn around just before they reached him after one of their horses broke through the crust of a hot spring. Finally, after nearly exhausting all their supplies, an unexpected snowstorm on September 13th compelled them to call off the search entirely. They began heading West to Virginia City along the Madison River, leaving at their campsite notes and what little supplies they could spare in the hopes he would find these caches, but he never did.
The following weeks found the ill-fated and hapless Everts suffering a seemingly endless cascade of dreadful misfortunes and horrendous calamities. He lost both of his knives. During a multi-day storm, he was left drenched and freezing cold with his feet frostbitten. While sleeping, he burned both his hands in his campfire and went on to become horribly scalded on his hip after breaking through the crust of a hot spring. The desperate Everts even spent a night high up in a tree, attempting to save himself from a mountain lion growling and circling the base of the tree below.