Ancient Southwest is a region Camp
Internet defines as containing
what are now Arizona, New Mexico, Utah, Colorado, Southern Nevada, Western Texas, Southern California, Baja California, and North Western Mexico. Before humans arrived to define these lands with state and national boundaries, they were and still remain a fascinating region defined by its unusual geography, and also by its watersheds, primarily the watershed surrounding what is now the Colorado River as it heads south to empty into the Gulf of California.
Imagine yourself up in orbit above the earth, looking at the Southwest. You would be able to see the path of the Colorado as it crosses the Colorado Plateau from the north to the south. It would be one of the central visible focal points in the region. Study how its looks today, and imagine how it looked in ancient times. To the west of the lower Colorado River are now the deserts, inland and coastal ranges, and basins of Southern California. But for millions of years those areas were actually a shallow seabed beneath the Pacific Ocean, and what is now Arizona was the Pacific shoreline. Before the Colorado Plateau rose to its current height, at times even Utah in the north was also under a sea of water that filled down into lower elevations from the Arctic. To the east of the Colorado, another major river defines a secondary watershed, that of the Rio Grande that flows down to the Gulf of Mexico through the Rio Grande Rift in the Colorado Plateau. All together, the region spans from where the Rio Grande empties into the Gulf of Mexico in the east, across to where the Colorado reaches the Gulf of California, to the far west of the continent and out to the Channel Islands.
Southwestern geography now includes five regions: The Colorado Plateau in the North,
the Sonoran Desert in the south extending down into Northern Mexico and Baja California, the Mohave Desert to the West, the Inland valleys and coastal ranges of Southern California including the Channel Islands offshore and, to the east, the northern reaches of the Chihuahua Desert in southern New Mexico and western Texas.
But again, it is the rivers that define the region, the Colorado River and the Rio Grande. You might think that rivers seem less of an enduring or defining geographic feature than the stunning and seemingly eternal canyons, tall mountains, and vast deserts of the Southwest. But these quiet perpetual bodies of water hold one of the greatest powers that shaped the Ancient Southwest landscape. The other major power was the plate tectonics turning the single massive continent of Pangaea into the multiple continents we know today, pushing, lifting, smashing land masses and causing violent earthquakes, rising mountain ranges, and periodic volcanic eruptions.