Ahead you can see where the creek joins the Rio Grande, which is partway along its journey from Colorado through New Mexico, tracing the Texas- Mexico border, to the Gulf of Mexico. The river flows through basins formed by spreading of the earth’s crust along the Rio Grande Rift, a feature at least 30 million years old. The mountains on the far side of the river are the Cerros del Rio (SER-ose del REE-oh), which is Spanish for Mountains of the River. These mountains are volcanoes which, over the last 1 - 3 million years, produced the basalt rocks through which you have been walking. In many places on the sides of the canyon you may notice evidence of the passage of time between eruptions. Here and there a layer of very red dirt appears. This is soil that formed through time and erosional processes on the surface of one flow, and then was covered by the next one. The heat of the new lava flow baked the soil, producing the red color.