3 aasa 3345 3309 3445 3434 3335 12 A Coulee M 3342 Blackfeet FIGURE 8.6 Portage, Montana 0 1 2 0 1/2 1 Sheffels M MISSOURI 2309 32 3370 Gulch 37 Boxelder Creek 3407 North 10 3 kilometers 2 miles Figire 8.6 SCALE: 1:62,500 336 RIVER 34 Q 35 J 3439 CONTOUR INTERVAL 20 FEET DATUM IS MEAN SEA LEVEL BM CASCADE CO CHOUTEAU.CO SELT cas Salem Sch Cleate 19 24 25 30 MONTANA QUADRANGLE LOCATION 3.5 3.0- 2.5 2.0- 1.5 1.0- A.O A.5 0.5 mile B.O Figure 8.7
Use the Portage, Montana, topographic map in Figure 8.6 (on page 136) and the stereogram in Figure 8.7 (on page 137) to complete the following.
1. Compare the stereogram in Figure 8.7 to the map in Figure 8.6. Then, on the topographic map, outline the area shown in the photo.
2. Is the terrain in Section 14, located on the west side of this map, relatively flat or hilly? Explain.
3. Label the areas that topographically resemble Section 14 on the topographic map as "upland."
4. Describe the topography in the lower half of Section 17, located three sections east of section 14.
5. Section 17 contains a portion of the valley occupied by the Missouri River. Approximately what percentage of the area shown on the map is stream valley (similar to the lower half of Section 17) and what percentage is upland?
6. Which of the following best describes the shape of the Missouri River Valley along the line labeled D.-D': wide valley with a floodplain or steep-sided V-shaped valley with no floodplain?
7. Calculate the gradient, or slope, of this portion of the Missouri River by following the steps below:
Step 1: Locate a contour line that crosses the river. Note: An index contour crosses the river in Section 26 (lower left portion of the map). Follow the index contour to the right to establish its elevation.
Step 2: Locate a second index contour that crosses the river. Note: Look in Section 11, between the letters V and E in the word RIVER. What is its elevation?
Step 3: Use a string and the bar scale to measure the approximate distance (to the nearest mile) between these two index contours.
Step 4: Calculate the gradient of the river by using the following formula: Gradient Difference in elevation (feet) / Distance (miles)
8. Approximately how many feet is the Missouri River above sea level?
9. What are the features in the river labeled with the letter A? (Hint: See the inside front cover.)
10. Based on your answer to Question 9, are the Missouri River and its tributaries actively eroding or depositing in this region?
11. Over time, as tributaries erode and lengthen their courses in their headwaters, what will happen to the upland areas?
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