The potential violent power of flood waters of the San Antonio River during heavy or extended rainfall prompted the U.S. Army Corps of Engineers to create a huge, straight river channel almost a half a century ago. Although soils near the mission sites have a great deal of clay content, the soil is relatively shallow over limestone bedrock. There are deep alluvial soils in the former river floodplain; the mission labores were located there. Aggressive hydrologic activity can erode isolated sections of banks of rivers, streams and acequias. Man-made cement retaining walls along the river and streams are testament to this hydrologic activity.