The Critical Zone

Exploring Geologic Maps


Geologists use and create a variety of maps to display the results of our work. Among the simplest of these are maps of bedrock and surficial geology. Bedrock maps display the various rock types in a region. They are best understood if you can imagine stripping away all of the unconsolidated sediment, soil, and vegetation from the land surface down to solid rock. Bedrock maps do not indicate that XYZ rock type can be found at ABC locale; instead, they show what exists in the subsurface beneath the soil and sediment and vegetation. In some places, particularly out west, rocks do exist at the surface! In that case, the bedrock map shows the rock type at the surface.

Surficial geologic maps differ from bedrock maps in that they display the sediments mantling bedrock. In some places, no sediment exists and, therefore, the surficial map may show bedrock. But in others, for example in northeastern and northwestern Pennsylvania (where multiple glaciers dumped their sediment load over the past several hundred thousand years), surficial geologic maps differentiate between the various materials moved into the region by glaciation and may even differentiate between deposits of different ice ages.

Now let's take a look at the geologic maps available for your study site.



  1. Go to USGS AASG.
  2. Choose Map Catalog.
  3. Use the Google Maps/Location interface to find information for your study site. Use a similar approach as in the Groundwater study - bounding coordinates that are small, to begin with, but reach out further to find more information.
  4. From the check-box options provided, select bedrock and surficial under Geology heading, then click Search.
  5. Assess the available resources for your study site.
  6. Describe the results of your search and include bedrock and surficial geologic maps in a report no longer than two pages.
  7. Choose Resources and Hazards too—include a resource and hazard assessment of your site in the same report with all relevant maps.
  8. Save your document as either a Microsoft Word or PDF file in the following format:

    L8_geologicalmaps_AccessAccountID_LastName.doc (or .pdf).

    For example, student Elvis Aaron Presley's file would be named "L8_geologicalmaps_eap1_presley.doc"—this naming convention is important, as it will help me make sure I match each submission up with the right student!

Submitting your work

Upload your report to the "Lesson 8 - Geologic Maps" dropbox in Canvas (in the lesson under the Modules tab) by the due date indicated on our Canvas calendar.

Grading Criteria

You will be graded on the quality of your writing. You should not simply write responses to the questions and submit them to me. Instead plan on writing a short stand-alone paragraph (or page or whatever you decide is necessary considering any constraints I might have placed on you) so that anyone can read what you've written and understood it. You should strive to be specific and complete in responding to the questions. Your answers should be analytic, thoughtful and insightful, and should provide an insightful connection between ideas. The writing should be tight and crisp with varied sentence structure and a serious, professional tone.