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Lab 01 Topographic and Geologic
Maps
Dr. Gregg Wilkerson and Michael Oldershaw
Learn How To Use These Maps
Determining Location• Latitude and Longitude
• Public Land Survey System
Determining Elevation• “See” the Shape of Earth’s Surface
• Allows Identification of Geologic Features
Determine Rocks, Contacts and
Structures
1° = 1/360 of a
circle
1° = 60’(Minutes)
1’ = 60”(Seconds)
On some measurements we will get to the nearest 15”
You may also see “Mils”, short for “Mil Radian”, used by
militaries (there are 2 Pi Radians in a circle, divided by 1000,and
you get 6283 mils in each circle).
This Classroom is ~ 35°24’30”N Lat,118° 58’15”W
Lon
Now We’ll Use the Maps
Superimposed Grid over the Earth
Start with an arbitrary point of origin• Mount Diablo in the Bay Area (MDBM)
• Mount San Gorgonio near San Bernadino (SBBM)
• Mount Pierce near Humboldt (HBM)
Count each row (“Township”) north or
south
Count each column (“Range”) east or
west
Scale• Relation of map to real world
• Fractional Scale (1:24,000 or 1:62,500)
• Graphic Scale
• Verbal Scale
• Lat/Lon Scale (How many Minutes?)
Naming the Maps, Publication data
Adjacent Maps (two ways)
Magnetic Declination
Elevation relative to Mean (average) Sea Level
Depicted on “Topo” Maps with brown contourlines
Each contour is a line of equal elevation
Index Contour Line = heavier lines with labels,every
fifth line
Contour Interval = elevation change with each line (40’,
80’ most common)
Closely vs. widely spaced contours
Most of our maps are in feet, few in meters
Geology Lab
River Elevation
Canyon (note“Vs”)
Relief = High – Low elevation; total
elevation change for a map or area
Gradient = Average Slope;Rise/Run• (Elevation difference/Distance)
Topographic Profile = Graphic
representation of elevation change,
essentially a cross section of the surface
shape.
“Tick” Marks indicate decreasing elevation
Depict the rock types and structures at the surface
Show the relationships of these units (contacts)
Each map has a legend with rocks listed by age (oldest on the bottom, scale on side), and may be in the description
Each rock unit is distinguished by color and symbol
The legend depicts other symbols as well, including contacts, and structures (faults, folds)