Using Geologic Maps

The distribution of materials at and below the land surface affects everyone who lives on this planet. In Maine, earth materials control everything from searching for ground water to siting a house foundation to protecting the environment to mining for precious gems. To make informed decisions, there needs to be a system which portrays the complicated pattern of rocks and earth materials which form the land surface. Geologic maps fill this need, portraying information such as the distribution of rock types and unconsolidated materials such as clay, sand, and gravel; landslide and erosion hazards; ground water availability; and much more. Browse the following pages to find out how to become a more informed reader of geologic maps.

Making Geologic Maps - the STATEMAP Program

The Maine Geological Survey (MGS) conducts geologic mapping throughout the state to provide landowners, planners, government agencies, educators, and industry with basic geologic resource information. Mapping projects are prioritized every year by the state’s Mapping Advisory Committee which are then funded through the U.S. Geological Survey National Cooperative Geologic Mapping Program’s competitive STATEMAP grant program and matching state funds. Geologists head out into the field spring through fall to observe and interpret geologic features in the selected areas. Work is completed by MGS staff geologists as well as contractors that are usually college professors and their students, so these mapping projects are also a way to mentor and educate new geologists. Mappers work from public roadways but also rely on the cooperation of towns and private landowners to access bedrock (ledge) and sediment exposures (such as gravel pits) to ensure accurate geologic interpretations and useful maps. Over the winter, observations and interpretations are compiled to create maps at the 1:24,000 scale (also referred to as detailed scale), which are usually finalized and published within the next year and available for free from MGS. MGS produces separate bedrock and surficial geology map series – details about these maps are their uses can be found in links below. Lastly, information collected during mapping projects is often used to create geologic guides for publicly accessible areas as part of the very popular Geologic Facts and Localities series.

Reading and Understanding Geologic Maps

Reading Maps with a Critical Eye: Becoming an Informed Map Reader

Use the links in the following list to learn more about the geologic maps produced by the Maine Geological Survey. The Description link will provide a description of the map series, and links to the map explanation and sidebar. The How to Read link will provide tips on how to read the geologic map.

Bedrock Geology
   Map series Description How to read
   Bedrock View View

Coastal Marine Geology
   Map series Description How to read
   Bluffs View View
   Marine Geologic Environments View
   Coastal Sand Dune Maps View View
   Inner Continental Shelf View

Economic Geology
   Map series Description How to read
   Peat Resource Evaluation View

Geologic Hazards
   Map series Description How to read
   Landslide Hazards View View
   Landslide Susceptibility View

Surficial Geology
   Map series Description How to read
   Surficial - detailed View View
   Surficial - reconnaissance View
   Surficial - 1:250,000 View
   Surficial Materials View View

Water Resources
   Map series Description How to read
   Sand and Gravel Aquifers View View
   Bedrock Ground-Water View
   National Wetlands Inventory View

Last updated on May 1, 2020