Steptoe’s Buried Butte

Steptoe Butte is an extraordinary island of quartzite surrounded by much younger Columbia River Basalt and loess, located in the Palouse region of Whiteman County. The term Steptoe is after the name of Colonel Edward Steptoe, an army Lieutenant. The discovery of gold in the Colville region promoted an influx of white miners to the region, some of whom abused Native women. When the Indians killed several of the miners in response, Steptoe was dispatched to intimidate the Natives. The soldiers had limited ammunition and were not expecting to encounter a united front of armed warriors from from the Yakamas, Spokanes, Coeur d’Alenes and the Palouse tribes. A running battle resulted in seven casualties on Steptoe’s side retreat back to Fort Walla Walla (Emerson, 2008).

The name Steptoe is now commonly used by geologist to describe a reclusive mountain or hill of ancient rock surrounded by younger geological formations (see photo of Steptoe Butte). The butte of quartzite is well over 400 million years old, metamorphosed from a protolith of sandstone that went under searing temperatures and pressure into a hardy metamorphic rock known as quartzite which is almost entirely made of interlocking grains of quartz and other minerals (see photos of quartzite). On the northern lower part of the miraculous summit, it has vitreous quartzite with feldspathic matrix that was initially interpreted as Precambrian Belt Supergroup (Waggoner, 1998 and the attached geologic map). But, using the age distribution of detrital zircons resulted in a dominant age peak of 1.7 to 1.9 billion years old (Ellis et al., 2004), which correlates with the age peak of detrital zircons from the Cambrian period (e.g. Ross and Villeneuve, 2003; Linde et al, 2017). This information means that the quartzite is not as old as it was once thought to be, but is still quite old.
Even though the butte is not dated in the Precambrian it is still one of the oldest geological sites in Washington state. Relatively recent a basalt flood submerged a large portion of the northeastern part of the U.S. about 16 million years ago and covered over 81,000 square miles (Kasbohm and Schone, 2018). After the Columbia River Basalt floods during the last ice ages (peaking about 16,000 years ago according to Balbas et al., 2018) pulverized rocks into an excessive amount of fine sand known as loess. The silt and dust from the glacier outwash blew in and buried the basalt, forming up to 200 feet tall hills of loess that make up the Palouse and its world-class agriculture- soils (see photo of Palouse hills). Even after that large area was submerged by the flood and then covered in loess Steptoe’s peak still stands over 984 feet above the landscape, dominating the horizon of the Palouse.

Images

Map