Walters Bar Area Topographic Mapping
activity exercisesuggested grade levels: 9-12
view Idaho achievement standards for this lesson

Overview:
Topographic maps are tools used in geologic studies because they show the configuration of the earth's surface.

Procedure:
Topographic maps are tools used in geologic studies because they show the configuration of the earth's surface. Horizontal distances and vertical elevations can be measured from a topographic map. Contour lines are used to determine elevations and are lines on a map that are produced from connecting points of equal elevation. Elevation refers to height in feet (or meters) above sea level. The following are general characteristics of contour lines:
1.Contour lines do not cross each other, divide or split.
2.Closely spaced contour lines represent steep slopes, conversely, contour lines that are spaced far apart represent gentle slopes.
3.Contour lines trend up valleys and form a "V" or a "U" where they cross a stream.
On most topographic maps, index contour lines are generally darker and are marked with their elevations. Lighter contour lines do not have elevations, but can be determined by counting up or down from the nearest index contour line and multiplying by the contour interval. The contour interval is stated on every topographic map and is usually located below the scale.

Review
1. Find Celebration Park Visitors Center on the north bank of the Snake River. What is the elevation at this point? If you walk to the southeast across the Snake River and hike up Guffy Butte you are at what elevation?

Topographic Profile
Topographic maps represent a view of the landscape as seen from above. For producing a detailed study of a landform it is necessary to construct a topographic profile or cross-section through a particular interval. A profile may be constructed quickly and accurately across any straight line on a map by following this procedure.

a. Lay a strip of paper along a line across the area where the profile is to be constructed.
b. Mark on the paper the exact place where each contour, stream and hill top crosses the profile line.
c. Label each mark with the elevation of the contour it represents.
d. Prepare a vertical scale on profile paper by labeling the horizontal lines corresponding to the elevation of each index contour line.
e. Place the paper with the labeled contour lines at the bottom of the profile paper and project each contour to the horizontal line of the same elevation.
f. Connect the points.

2. Construct a topographic profile across Walters Bar.
Stream Gradient
Stream gradient can also be determined from a topographic map. The gradient of a steam or river is determined by measuring a section of a stream or river and dividing the distance (in miles) into the vertical difference (in feet) between the two points. The result is expressed in feet per mile (ft./mi). The equation used is: Gradient = drop in elevation between two chosen points (feet) distance between the two points (miles)
3. Determine the stream gradient for the Snake River using either map, but be sure to specify which you used!
4. Measure the width of the canyon on the Walters Butte 7.5' Quadrangle map.
5. Measure the depth of the canyon on Walters Butte 7.5' Quadrangle map.
6. What type of feature is Walters Butte?
7. What is the elevation of Walters Butte?

Related Lesson Topics:
Hydrology: Hydrology

Lesson Plan provided by Vita Taube, 2000
Idaho Achievement Standards (as of 7/2001) met by completing this activity:
351.02
357.01