The Meandering River
The Bryant and its major tributaries are very sinuous streams. The stream valleys and the stream channels within the valleys do a considerable amount of wandering or meandering back and forth. These "meanders" (Figure 1) are an erosional feature that is typical of a mature stream. The meanders of the Bryant are entrenched, that is they form deep meandering valleys that are two to three hundred feet deep.
The stream valleys are typically asymmetric. The outside
of the meander is normally a very steep slope or a bluff whereas the inside
of the curve is a much more gradual slope. The reason for this asymmetry
is simple physics. Along the outside of the curve the river is forced
to turn and the force of the moving water is concentrated along this bank
and erodes it away. The inside of the curve is a larger region of little
erosional force and is the site of deposition. Gravel bars typically are
found along the inside curve of a meander. The river channel will move
laterally over time in the direction of the outside curve of a meander.
This causes the meanders to grow more pronounced with time.
A very interesting feature is found at the junction of Bryant and North Fork. Pine Hill (Figure 2) is an elongated triangular hill just to the north of the junction. Around the north side of Pine Hill is a semicircular valley that is actually a dry meander. At one time the North Fork actually went around Pine Hill in a very tight meander. The junction between Bryant and North Fork at that time was probably in the vicinity of Parker Cemetery. Lateral erosion along the outside curves at the neck of the meander finally cut through the narrow ridge between creating a "cutoff meander" that now loops around Pine Hill. This cutoff probably occurred several thousand years ago.
A fault has been mapped by the U.S. Geologic Survey which goes through the long dimension of Pine Hill (Fig. 3). This fault may be the reason that this long narrow meander developed here (see below).
Although most meanders observed in the Bryant and its tributaries probably developed by a normal erosional process, there are a few whose features are different enough to require a different explanation.
Several strands of the Mansfield Fault Zone have been mapped in this area and apparently cross the Bryant and Dry Creek courses. It appears that movement on these faults may have caused deflections of the streams or the fault zones have created resistant zones that caused the deflection of the streams and resulted in the unusual meanders. The geologic map of the area (Figure 5) shows a number of faults in the local area.