LANDSLIDE MAPPING ALONG THE INTERSTATE 17 CORRIDOR, CENTRAL ARIZONA

Landslides occur in a variety of landscapes and geologic settings throughout Arizona. Prior to 2015, our knowledge of the number and distribution of these slides was limited and scattered across many geologic maps and reports. In 2015 the Arizona Geological Survey (AZGS) compiled the Arizona Statewide Landslide Inventory Database (AzSLID) which included all known mapped and published landslide deposits throughout Arizona. Many additional, previously unmapped landslides were identified in aerial imagery and topographic data during this process. These interpreted features were included in AzSLID but no field verification was conducted.

In 2019, AZGS began a new project to study the character and extent of landslide deposits along I-17 from Anthem to Flagstaff, using a combination of field mapping and high-resolution topography. This study area was chosen because of the potential high impact landslides may have on existing infrastructure as well as upcoming plans to expand I-17 near Black Canyon City; an area with many mapped landslides. Damage to roadways by landslides can be catastrophic and extremely expensive to repair and mitigate. In 2008, a section of AZ State Route 87 was damaged by a reactivated portion of a larger slide cut by the road. In 2013, a similar failure within the Bittersprings landslide resulted in the destruction of a portion of US 89. Assessment, repair, and reroutes associated with these events totaled $18M, and $60M, respectively.

The results of this study include verification of interpreted AzSLID landslides, more detailed and refined mapping and descriptions of landslide deposits, and discovery of previously unknown landslide deposits. Clusters of landslide deposits were encountered where the geologic setting was favorable, generally along the edges of high-relief mesas with erosion-resistant caps overlying unconsolidated sediments. Notable new landslide locales include the Verde Valley and Lake Mary fault zone in upper Walnut Canyon. These improvements to our knowledge of landslides in high-impact areas along I-17 will be useful for hazard assessment and planning. All landslide mapping is available for viewing and download on the AZGS Hazard Viewer online.