San Diego Mountain, also called Tonuco Mountain, rises on the east bank of the Rio Grande in southern New Mexico and became important chiefly because of its location along major travel routes. It marked Paraje de San Diego, a Spanish campsite on El Camino Real de Tierra Adentro and the last place to draw Rio Grande water before a long dry stretch to Paraje de Fray Cristóbal. The mountain later identified the area of San Diego Crossing, where a cutoff from El Camino Real crossed the river to connect with Cooke’s Wagon Road. The vicinity was also associated with Camp Garland and later Fort Thorn, reflecting its lasting role in travel through the Rio Grande corridor.