As the expedition left to ascend the mountain, a long pack train of nearly fifty officers, soldiers and native guides departed from the town of Orizaba in early May 1848. After several days of hiking through dense jungle, the expedition slowly gained altitude and established a base camp at . Starting from base camp in the early morning of May 10 nearly two dozen climbers made the final push to the top of the mountain, but only Raynolds and a few others reached the summit. According to mountaineer and author Leigh N. Ortenburger, this feat may have inadvertently set the American mountaineering altitude record for the next fifty years. Raynolds estimated the summit of Pico de Orizaba to be above sea level, which was slightly greater than previous estimates but below the modern known altitude. As no higher peaks were known in North America at that time, Raynolds believed Pico de Orizaba was the tallest mountain on the continent. The summit crater was covered in snow but estimated to be between in diameter and deep. The American achievement was disputed by the Mexicans until an 1851 French expedition discovered an American flag on the summit with the year 1848 carved in the flagpole.