 When war with Mexico seemed imminent , topographic engineers were sent to the border to assist with the army 's preparations . Raynolds served in Winfield Scott 's Mexican @-@ American War campaign which marched overland to Mexico City from the Gulf of Mexico seaport at Veracruz . After the war , the American army occupied Mexico City and the surrounding region . During the occupation , Raynolds and others set out to map and explore nearby mountains . Raynolds 's party is credited with being the first confirmed to climb to the summit of Pico de Orizaba ( 19 ° 01 ′ 48 ″ N 97 ° 16 ′ 12 ″ W ) which at 18 @,@ 620 feet ( 5 @,@ 680 m ) is the tallest mountain in Mexico and third tallest in North America . Over a period of several months , Raynolds and other officers from both the army and navy mapped the best approach route to Pico de Orizaba . To assist them in their climb , the party planned on taking grapnels attached to long ropes and primitive crampons in the form of shoes with projecting points to help ensure they could safely climb up cliffs and across glaciers . Told by local villagers that any attempt to reach the summit would be fruitless because no one had ever done it before , the Americans became even more determined to show the Mexicans it could be climbed . 
