OF-95-05 The Dipping Bedrock Overlay District (DBOD): An Area of Potential Heaving Bedrock Patterns Associated with Expansive, Steeply Dipping Bedrock in Douglas County, Colorado


Detailed examination of this prominent geological hazard in Douglas County. 32 pages. 1 plate. Digital PDF download. OF-95-05D

Heaving bedrock — a distinctive geological hazard related to expansive soils but more complex in nature — is responsible for tens of millions of dollars worth of damage to homes, roadways, and utilities along the Front Range piedmont of Colorado. In Douglas County alone, several million dollars worth of damage has been incurred since suburban-type development began in the mid-1980s. Large undeveloped areas which are underlain by potentially heaving bedrock warrant special consideration during all phases of site planning and development, and, in some cases, avoidance may be the most advisable land use alternative.

The geographical area where heaving bedrock hazards are anticipated, and where problem-specific regulations and requirements are applicable, is effectively shown in the form of a geologically defined overlay map. The CGS has delineated an area of Douglas County, called the Dipping Bedrock Overlay District (DBOD), where heaving bedrock hazards are anticipated. The DBOD is based upon the overlapping presence of two regional-scale geological attributes: 1) steeply dipping sedimentary bedding, with dip angles of greater than 30 degrees from horizontal, and 2) zones of bedrock which expand when excess moisture is introduced (expansive bedrock).