The territorial boundaries along the 37th Parallel were originally surveyed by J.E. Weyss (Kansas-Oklahoma), in 1857, Ehud Darling (Colorado-New Mexico) in 1868, and Howard Carpenter (Arizona-Utah) in 1901. The map details below indicate how little was actually known about the landscape upon which the border lines were to be drawn.
‘Map of the Territory of the United States from the Mississippi to the Pacific Ocean’ ordered by the Hon. Jeff’n Davis, Secretary of War… compiled by Lieut G. K. Warren, Topl Engrs, … 1855. The red line is drawn on the 38th Parallel. The map appears to be incomplete: territory west of the Sangre de Cristo mountains– what would become the 37th parallel borderlands– evidently had not been explored when the decision to draw the borders at 37 degrees north latitude was made. Source: Schulten, Susan, Mapping the Nation. See mappingthenation.com.