Lab 8: Mapping - Example Topographic Maps

 

First a little bit of info on the most common contour maps geologists use, topographic maps. You can search the Internet and find many example sites, but one good one is topozone.com. Here are a few places to check out, along with an explanation of doing a topographic profile.

 

If you visit topozone.com, change the scale fro 1:500,000 to move around in big jumps, then set it to about 1:100,000 for most viewing needs. After finishing this lab, look at examples on the Internet until you are confident that you can identify basic features discussed in the lab, and how to interpret and visualize contour lines and the landscapes they represent. It will take some practice. Also, for topozone.com, if your computer screen is large enough, you can set the Map Size to Large.

 

For the examples below, Bone Canyon and Apache Canyon in far west Texas, see the map below for their locations:

 

Texas with Bone and Apache Canyons Labeled (far left, center)

 

Bone Canyon

 

This is one the western side of Guadalupe Peak, the highest point in Texas. The Guadalupe Mountains are located in far western Texas, up against the southern border of New Mexico. Just "up the hill" is Guadalupe Peak , at an elevation of 8749 feet. You should be able to make out the canyon easily, with the strong veeing of the contours, up the notch cut by erosion. Click the link at the beginning of this paragraph to go to topozone.com to scroll around the map.

 

 

In the photograph above, North is toward the left, but in the map below, North is toward the top. So, you'll need to realize that the axis of the canyon, which is easy to see by the vees in the contours on the topographic map below, runs up the side of the mountain, toward the arrow pointing out the canyon in the photograph (Rotate the map 90 degrees counterclockwise in your head). Note the use of index contours (bold) to make the map easier to read. The contour interval of the map is 20 feet, and the index contour interval is 100 feet. You see numerous noses (nosing contours) on the map, where harder rock layers form ridge extensions and small platform areas along the slope of the mountain.

 

 

Apache Canyon

 

This is a long canyon cutting through Sierra Diablo, near the boundary of Hudspeth and Culberson Counties, in far west Texas, just to the south of the Guadalupe Mountains. The first topographic map is at a scale of 1:200,000, and the second shows more detail for the canyon. The canyon was named after the Mescalero Apache, as described in this little write-up . Click the link at the beginning of this paragraph to go to topozone.com to scroll around the map. The contour interval of the map is 20 feet, and the index contour interval is 100 feet. The closer spacing of the contours along Apache Canyon, of course, shows the steeper terrain along the canyon sides.

 

 

 

On the satellite image above you will hopefully find Apache Canyon. Note the large alluvial fan at the end of the canyon. Look back at the first topographic map of Apache Canyon and you'll see the telltale signature of the alluvial fan's shape in the wide, apron-shape of the contours in the upper right corner of the topographic map. The image below shows the topographic map overlain on the satellite image, if you need help finding the canyon and the alluvial fan.