Clumps of spear-like cacti that give the park its name are scattered throughout -- occasionally in greater concentration -- within Organ Pipe Cactus National Monument, a 517-square-mile reserve that shares a border between Arizona's Yuma County and the Mexican state of Sonora. The park is the only place in the United States where the organ pipe cactus grows wild. Along with organ pipe, many other types of cacti and other desert flora native to the Yuma Desert grow in the park