An exhumed river channel is a ridge of

sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates ...

that remains when the softer flood plain mudstone is

eroded Erosion is the action of surface processes (such as water flow or wind) that removes soil, rock, or dissolved material from one location on the Earth's crust, and then transports it to another location where it is deposited. Erosion is disti ...

away. The process begins with the deposition of sand within a

river A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases, a river flows into the ground and becomes dry at the end of its course without reaching another body of w ...

channel (typically a

meander A meander is one of a series of regular sinuous curves in the channel of a river or other watercourse. It is produced as a watercourse erodes the sediments of an outer, concave bank ( cut bank) and deposits sediments on an inner, convex ba ...

ing river) and mud on the adjacent

floodplain A floodplain or flood plain or bottomlands is an area of land adjacent to a river which stretches from the banks of its channel to the base of the enclosing valley walls, and which experiences flooding during periods of high discharge.Goudi ...

. Eventually the channel is abandoned and over time becomes buried by flood deposits from other channels. Because the sand is porous (grain-to-grain contact leaves spaces between),

groundwater Groundwater is the water present beneath Earth's surface in rock and soil pore spaces and in the fractures of rock formations. About 30 percent of all readily available freshwater in the world is groundwater. A unit of rock or an unconsolidated ...

flows more easily through the sand than through the mud of the floodplain deposits. Minerals (typically calcium carbonate) can cement the grains together converting the loose sand into sandstone. Meanwhile, pressure from overlying

sediment Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sa ...

s compresses the floodplain mud converting it to mudstone. Millions of years later, erosion can remove the softer, less cemented mudstone and leave the more resistant sandstone as a sinuous ridge. Thus, an exhumed river channel is a form of

inverted relief Inverted relief, inverted topography, or topographic inversion refers to landscape features that have reversed their elevation relative to other features. It most often occurs when low areas of a landscape become filled with lava or sediment th ...

: what was previously low is now high, and vice versa. Exhumed channels are important indicators for ancient stream flow direction. Some of the best examples of exhumed river channels occur in the Ruby Ranch Member of the

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...

Cedar Mountain Formation The Cedar Mountain Formation is the name given to a distinctive sedimentary geologic formation in eastern Utah, spanning most of the early and mid- Cretaceous. The formation was named for Cedar Mountain in northern Emery County, Utah, where Will ...

southwest of Green River, Utah. Within the Cedar Mountain Formation in this part of Utah, fluvial

s filling paleochannels within it are cemented by calcium carbonate. Because of this cementation, the sandstone filling these paleochannels are considerably more resistant to erosion than the shale and mudstone that enclose them. As a result, differential erosion preferentially removes the shale and mudstone and exposes these paleochannels as ridges.Williams, R.M.E., T.C. Chidsey, Jr., and D.E. Eby, D.E., 2007
''Exhumed paleochannels in central Utah - analogs for raised curvilinear features on Mars''
in G.C. Willis M.D. Hylland, D.L. Clark, and T.C. Chidsey, Jr., eds., pp. 220-235, Central Utah - diverse geology of a dynamic landscape. Publication 36, Utah Geological Association, Salt Lake City, Utah.Harris, D.R. 1980
''Exhumed paleochannels in the Lower Cretaceous Cedar Mountain Formation near Green River, Utah.''

Brigham Young University Brigham Young University (BYU, sometimes referred to colloquially as The Y) is a private research university in Provo, Utah. It was founded in 1875 by religious leader Brigham Young and is sponsored by the Church of Jesus Christ of Latter-d ...

Geology Studies 27:51–66..

References

{{reflist Geomorphology Erosion landforms Sedimentology