Kotenai Formation

All the mapping areas surrounding Dillon has the youngest unit of the Quaternary period, which is the alluvial sediment. Alluvium sediment is an unconsolidated deposit of clay, silt, sand and gravel as a result of stream flows in a river valley or delta. The unlithified deposits fill a basin and lump together to form ‘alluvial’ sediments. Other Quaternary depositions include talus and landslide. Talus occupies both Block Mountain and Timber Hill, while landslide only occupies Block Mountain. Talus is an accumulation of broken rock fragments at the base of valleys or mountain cliffs. The accumulation forms scree slopes or talus piles, which make up a cone shape corresponds to the angle of repose. Landslide sediment is nonconsolidated sediment …show more content…
Kootenai Formation consists of Gastropod Limestone, Upper Clastic, Middle Limestone and Lower Clastic. Gastropod limestone is typically dark gray or white when exposed, and the new rocks are in either gray color or sparkly crystals, indicating the calcium carbonate. The grains of the carbonate stones vary from fine to sand-sized. This member of the Kootenai formation preserves fossils such as gastropods that date back to the late Cretaceous period. Gastropod Fossil is from the mollusk class, and it leaves spirally and convex-shaped casts within the beds of the limestone. The rocks in this formation are resistant, and they usually form on high ridges. The second member of Kootenai is the Upper Clastic, which exhibits red to orange colored soils. The grains of this clastic stone vary from fine to sand-sized. They have finer grains than the Lower Clastic unit, due to different deposition environments. The third member is the Middle Limestone, which consists of compacted and precipitated calcium carbonate. Rocks within this formation range from gray to white when exposed, and the new rocks are in either light brown, yellow or green color, with pieces of plant materials (ostracod fossil). The grains are very fine, and they would form clay. These fine-grained rocks are highly erodable and are recessive towards weathering. Since the rocks in this formation are recessive, they usually found in the valleys. Lower Clastic consists of …show more content…
The Morrison Formation of the Jurassic period overlaid this Formation in most mapping areas. Upper Dinwoody Formation consists of brownish to orange rocks when exposed, and the new rocks are in either gray color or sparkly crystals, indicating the calcium carbonate. Dinwoody Formation preserves fossils such as Claraia that dates back to the early Triassic period. Claraia fossil is a shelly fossil that leaves thin, rounded and convex-shaped casts within the planar beds of limestone. Upper Dinwoody rocks are typically resistant and form on high ridges, while Lower Dinwoody is recessive and found in the

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