Union

Union, county, northeastern New Mexico, U.S., bordered on the north by Colorado and on the east by Oklahoma and Texas. It lies in the Great Plains. The eastern landscape is marked by black-capped mesas and the twin Rabbit Ear Mountains, ancient volcanic vents that became a landmark on the southern fork of the Santa Fe Trail. In the west are two volcanos, Sierra Grande and Capulin Mountain. Dry lakes and arroyos scar Union county, but...