About 1.1 billion years ago, a great rift valley formed across the North American continent from the Lake Superior region southwest to Kansas. As this rift valley opened, basaltic lavas erupted into it, accumulating to a thickness of up to 20 kilometers in the Lake Superior region. The dark-grey basalt rock that form the St. Croix River gorge are made from these rift lava flows. Continental rifting with volcanism is common in the geological record and often leads to the breakup of continents and the formation of intervening ocean basins. For reasons not completely understood, the Midcontinent Rift here in North America failed to evolve to the stage of complete continental separation.
About 520 million years ago in the Lake Cambrian period, the North American continent was positioned with Minnesota near the equator. Shallow seas covered the region, into which great thicknesses of mainly quartz sand were deposited. These deposits are now the sandstone bluffs along this river valley and the rock faces exposed on the highway road cuts south of this marker. Although most of the region then lay flat, the basalts in the Taylor Falls area stood high as rocky, cliff-ringed islands in a tropical sea.
The most recent geological event recorded here occurred about 12,000 years ago during the end of the Ice Age of the last two million years. As the last of the glaciers melted and receded to the north, tremendous quantities of sediment-laden glacial meltwaters were channeled into the St. Croix River valley. Here at Taylor Falls, a colossal torrent of abrasive currents carved down through the Cambrian sandstones and deep into the rift basalts now seen on the valley floor. The spectacular potholes in the lava rock, found in Interstate Park about 0.4 kilometers north of this site, attest to the high velocity of the raging glacial waters that carved the St. Croix River gorge.
Erected by the Geological Society of Minnesota in partnership with the Minnesota Department of Transportation and the Minnesota Geological Survey 1998