Student Name:                                                                                                  Grade:      

                                    Physical Geology 101 Laboratory                 

                                              Geology Maps

 

Introduction & Purpose:  The purpose of this lab is to both learn and apply the concepts of

structural geology to reading and interpreting geologic maps.   The terms and concepts of geologic

structures, the application of structural geology to mountain building events, and the terms,

concepts, and techniques used to create and interpret geologic maps will be discussed.   The

usefulness of geologic will also be highlighted and discussed.

     The objective of this laboratory exercise is to become successful at applying the principles learned

in the topographic and structural geology labs towards the analyzing geology maps for solving surface and subsurface structural and geologic relations that may include a record of igneous, metamorphic, and sedimentary rock-forming events, mountain building deformation, and surface erosion.  

 

Part I – Reading and Interpreting a Geologic Map

   Introduction:

    A geologic map is a greatly scaled-down, two-dimensional abstract representation of the surface geology, structure, and relief of a geographic region of Earth, or even another terrestrial planet.  A geologic map typically includes most information found on a topographic map, but most importantly, includes color-coding regions and symbols that denote rock units, contacts, and other structural information.  Additionally, all the geologic color-coding and symbols are explained in the legend on a geologic map, including topographic and cardinal information.  

 

A. Reading and Interpreting a Geology Map

     Directions: Do a general examination of the entire geologic map of the Devil’s Fence Quadrangle.   Carefully examine the various rock units represented by the colored regions and related map symbols on the map that portray the surface geology of this area in Montana.  Note their shape, aerial extent, and the larger structural patterns formed by spatially- associated outcropping rock units.   Use the explanation to the left of the map to decipher the rock units, in terms of formation name, age, and lithology, and structural.    Also use the explanation to the left of the map to decipher the structural relations of the various formations, including strike and dip, folding, and faulting.   Finally, answer the following questions, based on your analysis of the Devil’s Fence Quadrangle.

 

Topographic Questions

1) Where in Montana is the Devil’s Fence Quadrangle located?   _____________________

2) What is the magnetic declination for this region?  ____________________

3) What is the map and verbal scale for this map? ________________________________________

4) What is the contour interval of this map? ___________________

5) How many square miles does this map cover? _______________________

6) What are the minimum and maximum elevations for this area?  Min = ________  Max = _______ 7)  What is the total vertical relief for this area?  __________________

8) Would you consider this area gentle, or rugged, in relief?  ____________________________

9) Does the topography (location and orientation of ridges and valleys) correspond to the location and orientation of geologic rock units _____  Describe an example ______________________________

10) What topographic feature does Devil’s Fence correspond with? _________________________

Geologic Questions

11)  List the major types of rocks exposed in this area, such as sandstone, schist or granite.  Include at least six rock types.  Note: Include at least one rock type from each of the three major rock groups.  ____________, __________, ______________, ___________, _____________, and ___________.  

12) What is the total range in age for the various rock types found on the map?  ___________ years

13) Name the youngest rock unit exposed in this area?   __________________________

14) Where is this youngest rock unit located on the map? __________________________________

15) Name the oldest rock unit exposed in this area?   __________________________

16) Where is this oldest rock unit located on the map? ____________________________________

17) This rock unit forms the center of what general type of deformational geologic structure, such as a fold or fault? (hint: notice the upside down “V” shaped pattern of rocks)  _________________.

18) If you wrote down “fold”, is it a syncline or an anticline?   ______________________

19) What information did you use to tell whether it was a syncline or an anticline?  _______________

________________________________________________________________________________

20) If it is a fold, is it a horizontal or plunging fold?    __________________________

21) If plunging, then which direction is the fold plunging?  Determine the bearing of fold axis _______

22)  Find the Colorado Formation.  This rock unit forms the center of what general type of geologic structure, such as a fold or fault? (Hint: notice the upright “V” shaped pattern of rocks)  ___________.

23) If you wrote down “fold”, is it a syncline or an anticline?   ______________________

24) What information did you use to tell whether it was a syncline or an anticline?  _______________

________________________________________________________________________________

25) If it is a fold, then is it horizontal or plunging fold?    __________________________

26) If plunging, then which direction is the fold plunging?  Determine the bearing of fold axis _______

27) How many distinct folds are found in this geologic map? _____________

28) Which two compass directions did the deviatoric stresses come from to cause the folding? _____

29) What type of rock makes up the Sagebrush Park stock?  ______________________________

30) Determine the timing between the intrusion of the Sagebrush Park stock and the regional folding event.  Did the intrusion occur before, during, or after the folding?  Note: 1) the age of folding; 2) the age of intrusion, and 3) the age of post-folding sedimentation and volcanism.  Explain your answer. _____________________________________________________________________________ _____________________________________________________________________________

 

 Part II - Geologic Map Laboratory Reflection

    Write a short reflection (about a paragraph length) about your experience in working with geologic

maps, and cross-sections.  Include what you learned from this laboratory; what was interesting; the problems and challenges you encountered; and how this lab was designed (the good and/or bad).