LANDSLIDE CHARACTERISTICS AND HAZARDS ALONG THE I-70 CORRIDOR NEAR WOLCOTT AND EAGLE, COLORADO

Several types of landslides and associated hazards are present along the Interstate 70 corridor near Wolcott and Eagle in central Colorado. These include rock and debris slides, rock and debris flows, and rock falls, which differ in character and potential hazards they present. For example, I-70 crosses the toe of a landslide complex near Wolcott and traverses run-out regions of debris flows north and northeast of Eagle. The Bellyache Ridge landslide complex occurs on a north-facing slope directly south of Wolcott along I-70 and consists primarily of chaotic deposits of very large to small Cretaceous sandstone clasts in a finer grained matrix. Much of the Bellyache Ridge complex appears to be relatively old and stable, but scarps in some parts of the complex imply younger reactivation and a small area of the complex slides almost yearly. The eastern part of the Bellyache Ridge complex also includes rock-flow landslide deposits derived from Late Cretaceous shale. Persistent buckling and cracking of I-70 indicates ongoing activity in this shaly, eastern part of the complex. The Milk Creek landslide complex is located along north-facing slopes about 2 mi northwest of Wolcott and I-70 and is entirely in Late Cretaceous shale units. Failure of these shales has produced large masses of deformed, but relatively intact, bedded shale within landslides that are similar to shaly landslides of eastern Bellyache Ridge. The intact, but deformed, character of the shale in these landslides suggests a deep-creep failure process. Some scarps and pressure ridges appear to be relatively young features, suggesting that episodic and (or) slow creep may be ongoing beneath parts of the Milk Creek complex. In addition to the landslide complexes mentioned, debris-flow deposits are also present along and near I-70 and they are particularly common along south-facing slopes north and northeast of Eagle. Old debris-flow deposits are deeply incised and cap ridges, whereas younger debris-flow deposits are incised into, and partly derived from, the older deposits. The differing types of landslide features and hazards of this region probably require differing types of remediation and mitigation. Geologic map data, aerial photography, digital elevation models, and Landsat imagery can be used to identify and characterize landslide deposits and hazards along this part of the I-70 corridor.