Moses Coulee in spring when everything is GREEN.

A number of dry basalt coulees course through Eastern Washington. Moses Coulee, like many other coulees and canyons, was carved from solid basalt by huge floods. These floods occurred at the end of the last ice age between 15,000 and 10,000 years ago by a giant lake in Montana- Glacial Lake Missoula. The lake was formed from immense quantities of meltwater, and was dammed by ice. When the ice dam broke loose during warmer periods, enormous floods were released across Montana, Idaho and Washington States. The floods from this lake did not happen only once, but up to 60 different floods occurred. This violent erosive force is responsible for creating many of the geological features of Eastern Washington including the 'scab-lands'- so called because the floods scoured much of the topsoil from underlaying basalt, and created coulees and canyons that cut across the otherwise flat landscape.

Harlen Bretz first proposed the idea of catastrophic floods in the 1920's to explain geological features in the Columbia Basin, but it wasn't until the 1970's that this idea was finally accepted by most geologists. One of the most important principles in geology, the principle of Uniformitarianism, was developed in the 1700's and states that processes that happened in the past also occur today, and the earth's features were shaped over long periods of time. Previous to this theory it was widely accepted that the earth was shaped by catastrophic events and occurred suddenly; this theory of catastrophicism was in agreement with the Christian view of the creation of the world and its age. Part of the reason that Harlen Bretz's theory of Lake Missoula floods was not accepted is the history of theory in geology. Geologists did not want to believe that a theory that was tossed out for a better explaination hundreds of years before could be right. It is now known that there have been several earth shaping events created by catastrophes such as meteors and floods, but the principle of uniformitarianism still remains the best answer to most geological formations and processes. Catastrophic flooding occurred throughout most of Eastern Washington, the tremendous force of the water created coulees and canyons out of solid basalt such as this and carried and deposited 10 ten ton boulders around like pebbles, leaving in its wake a vastly changed landscape. Floods from Montana may have occurred over 100 times in the course of 3 to 5 thousand years.

Although lower Moses Coulee has been the home of cattle ranching families for over 100 years, the coulee's vegetation remains in good ecological condition and maintains a diversity of plant species and unburned sagebrush. The Nature Conservancy has been working with ranchers, the communities involved and other organizations to maintain the coulee's unique geological and biological treasures for future generations.