Dry creek beds occur all over the world under a various assortment of names. In the United States, they are almost exclusively found in the arid and semi-arid regions of the Southwest. A dry creek bed can be very short, less than a mile, or extremely long with a length that approaches twenty miles or more. In Spanish, a dry creek bed is referred to as an arroyo, a very common term that you will find frequently used all across the southwest. Dry creek beds often appear as features on topographical maps, where they are often referred to as an arroyo or a gulch.
Dry creek beds are formed by the flow of water, so they always move in a downhill direction. The bottom of an dry creek bed will almost always be sandy and strewn with small, water-worn rocks and debris. There may be even be an abundance of small vegetation that thrives off the occasional moisture from the runoff. If soil conditions are right the side walls of a dry creek may be vertical.
At least two towns in the United States are named after dry creek beds. They are Arroyo Seco in New Mexico and Arroyo Grande in California. Other dry creek beds will appear on maps under the name of gulch. There are several state parks, some ranches and even a western theme park named after a gulch, a colorful term that is now firmly associated with the settling of the "American West."
A dry creek bed or arroyo is often a sign of fluctuation in local climate, but they can also be precipitated by man-made activities like grazing and excavation. A classic arroyo or gulch can form, when the climate in a particular section of the southwest goes through a prolonged wet cycle. The excess rainfall can transform the semi-arid landscape into a terrain etched with dry gulches or arroyos.
A dry creek bed becomes of critical importance during the rainy season, when flash flooding becomes a major concern. In many parts of the southwest flash flooding can occur at any time of the year. Having once witnesses a flash flood, it must be said that the dangers associated with this natural phenomenon have not been under-exaggerated. The physical force of a four foot wall of water that can come cascading down a dry creek bed (or arroyo) is amazing. Though it is true that flash floods are short lasting, their initial impact is tremendous and sometimes deadly. The waters make a roaring noise, when they approach, but the warning time can be as little as just a few seconds, depending on the terrain.
A dry creek bed can accumulate a huge volume of water in a short period of time in a very small area and then transport the raging torrent miles away, where the skies are blue and it is not raining.