The prairie region of North America once
formed the greatest grassland on earth. It covered nearly one-quarter of
the 48 states, along with portions of Canada and Mexico.
Crowning the northern part of this impressive landscape sits the prairie pothole region with its remarkable combination of wetlands and native prairies. Carved out by glaciers that retreated about 12,000 years ago, the 300,000 square-mile region harbored approximately 25 million depressions of varying sizes - an average of 83 potholes per square mile. This density of wetlands throughout rolling hills and flat river valleys was unmatched in North America.
These potholes were once set in endless expanses of native prairie. Three types of prairie once blanketed the region - shortgrass, mixed grass, and tallgrass in North and South Dakota, tallgrass in Minnesota and Iowa, and shortgrass in Montana. Historically, few trees adorned the prairies, due primarily to fire and a lack of sufficient moisture.
Pothole wetlands (temporary, seasonal, and permanent) in this region vary in size and type. They can range from a few feet across and only inches deep, to basins 500 acres in size with depths of over 10 feet.
Most basins receive their water from melting snow and rain; some are fed by groundwater. The amount of water they hold fluctuates with the amount of precipitation in any given year. During times of drought, many basins remain dry, and when rain is abundant, the landscape explodes in glistening blue basins.
