Even the state's bedrock foundation, whose picturesque ledges and bluffs outcrop along some of these river valleys, originated as layers of sediment settling out of water on ancient sea floors, along coastlines, and in stream channels millions of years ago. Iowa's past geological environments supplied the earth materials that contain our present surface and groundwater resources. These materials shape the forms that water takes on the land surface, and they also determine how fast and how far water moves underground and where it can be tapped for wells. They affect groundwater's natural quality, as well as its vulnerability to contamination introduced from the land surface. Photo by Photographic Services, The University of Iowa .
Water circulates through our environment in a process known as the hydrologic cycle .
Precipitation from clouds falls to the ground where it may be taken up by plant roots, flow as surface runoff to streams, or slowly percolate deeper into the earth to become groundwater. Water returns as vapor to the atmosphere primarily by evaporation from lakes and streams, and by plant transpiration. Photo by Photographic Services, The University of Iowa. This shallow marsh , with its lush aquatic vegetation, lies along the Iowa River floodplain at Otter Creek Marsh State Wildlife Refuge in Tama County. The sluggish backwaters persist in broadly curved lowland sloughs that were scoured by earlier meander channels of the river.