Memorial Falls
Montana USA
Memorial Falls drops over a ledge of the Precambrian Neihart Sandstone, which was deposited about 1,450,000,000 years ago. The waterfall is much younger, of course, probably initiated near the end of the last glacial period about 12,000 years ago. It’s located just off US Highway 89 about 2 miles south of Neihart, Montana USA, accessible on an easy half-mile (0.8 km) trail. It’s on Memorial Creek which flows into Belt Creek near the highway.
The Neihart formation is interpreted to be a thick sheet sand at the base of the Belt Supergroup, making it the oldest part of the Belt. As a compositionally mature quartz sandstone it is similar to the Cambrian Flathead Sandstone, although the latter is almost a billion years younger. The Neihart sand sheet is interpreted by some as a residual pile of sand that had been “stored up” on the pre-Belt erosional surface and which was reworked into the Neihart as Belt subsidence and deposition began about 1,450 million years ago (Schieber, J., 1989, The origin of the Neihart Quartzite: A basal deposit of the Mid-Proterozoic Belt Supergroup, Montana, U.S.A.: Geological Magazine, v. 126, p. 271-281).
The sand was largely fluvial (including some probable braided stream deposits on coastal plains), but some parts probably formed in nearshore environments (beaches and offshore sand bars, etc.). There is also evidence of some eolian (wind) reworking in parts of the Neihart.
Because the Neihart thickens to the west toward the middle of the Belt Basin, Schieber (cited above) interprets the Neihart to have been deposited in a gradually subsiding, sagging basin, the precursor to the more active rifting that ultimately separated whatever was present to the west from North America. According to Sears and Price (1978, The Siberian connection: A case for Precambrian separation of the North American and Siberian cratons: Geology, 6:267) it was Siberia that rifted away, but there are other interpretations for the ultimate origin of the Belt Basin.
If you are interested in my earlier Facebook posts about the geologic setting of 22 waterfalls worldwide, here’s a PDF compilation (12.8 megs). One from Australia, three from Iceland, three New Zealand, and the rest from the USA.
