About
Cedar Mountain SNA is one of a string of SNAs aligned along the meandering Minnesota River in Yellow Medicine, Renville and Redwood Counties. While each is unique, they share a common history, influenced both by the Des Moines lobe of the most recent glacial period and the subsequent torrent of Glacial River Warren.
Cedar Mountain is notable for being underlain by gneisses and diorite representing some of North America's oldest known bedrock—estimated to originate 3.6 billion years ago. The so-called "Cedar Mountain Complex" includes these ancient rocks and relatively younger (1.8 billion year-old) bedrock formed when magma flowed into cracks in the older rock. These igneous intrusives include two distinctive rock types described only from this location: Cedar Mountain Gabbro and Cedar Mountain Granodiorite, visible here in knobs and outcroppings.
Glacial River Warren left its mark on this site in many ways. All but the highest knobs here were inundated at some point during the river's flow. According to geologist Carrie Jennings in the Minnesota Biological Survey report Native Plant Communities & Rare Species of the Minnesota River Valley Counties, there were two time periods when this may have occurred, as Glacial Lake Agassiz drained to the south via Glacial River Warren. The first period was from roughly 14,000 to 12,900 years before present, and the second, roughly 11,000 to 9200 years before present.*
Researchers have estimated peak "catastrophic" flows of this monstrous glacial river at .364 Sv, which is equivalent to about 3000 times the modern-day baseflow conditions of the Minnesota River at Mankato.** The torrent swept away glacial sediments from the recent and earlier glaciations and left erosional features on the bedrock including scour channels, potholes and depressions of all sizes. Many of these "tracks" of Minnesota's glaciers and erosional features now hold small ponds, marsh-filled basins and ephemeral pools.
Today, the SNA reflects a calmer time. Visitors will find a rolling landscape dominated by oak woodland-brushland and mesic prairie. The low-lying, northern part of the SNA nearest the river features floodplain forest. Rock outcroppings support a number of rare plants, including devil's tongue (also known as plains prickly pear cactus) and waterhyssop.
Management here has focused on restoring a more open landscape, guided in part by historic 1938 aerial photographs of the site. Says SNA Regional Specialist Brad Bolduan, "It had become pretty overgrown. We've been steadily working to remove plum and cedar, along with doing some prescribed burns. Removal of invasive buckthorn and honeysuckle is the main emphasis in the near term. Long term, the aim is to bring back oak savanna and prairie where those communities previously occurred."
Water level changes can make it challenging to cross Wabasha Creek, near the southern boundary of the SNA. Access roads on the west side of the SNA (where the SNA adjoins Cedar Mountain Wildlife Management Area) are also subject to seasonal flooding.