The Bretz floods washed 300-400 feet of water over this plateau an estimated 100 times occurring some 12,000 to 15,000 years ago. These floods scoured everything down to bedrock. Later eruptions of Mt. St. Helens deposited four feet of ash on the plateau, which over time became "greasy clay" soil that today is arranged into the mysterious "mounds and swales" one sees while walking in the Tom McCall Preserve an area set aside and preserved by the Nature Conservancy. There are 321 acres protected on this plateau where the diversity of wildflowers can be seen from early March to the end of May. After the Bretz floods, along with the formation of mounds and swales a special type of soil developed called crytogamic soil. This is a combination of lichens, mosses, and fungi that also helped attract and encourage the unusual plant families that have made their homes on the Rowena Plateau.
We wandered slowly through a visual feast of yellow balsamroot, huge groupings of deep blue lupine mixed with many varieties of Buckwheat, not to mention the largest protected occurrence of Hood River milkvetch! Emerging from some of the drier mounds we found the heads of wild onions and the wonderful formations attached to a wild geranium called a Crane's bill.....it was a meandering through a complex and diverse botanical community with a backdrop of basalt cliffs descending down to the Columbia River.
