# 5.4: Lab Exercise (Part A)

## Part A – Drainage Patterns

Map 5.1, located on the next page, is a portion of a topographic map from Royal Gorge, Colorado, courtesy of the USGS. Study the map and answer the questions below.

1. What type of stream drainage pattern is present on this map? This may be easier to determine by examining the tributaries to the main stream.

a. dendritic                         b. trellis                         c. radial                         d. rectangular

2. Based on the drainage pattern type, does the bedrock underlying this area consist of rocks uniformly resistant to erosion or rocks alternating between resistant and non-resistant layers?

a. uniformly resistant bedrock                              b. alternately resistant and non-resistant bedrock

3. Are the rocks likely tilted and folded or horizontal?

a. tilted and folded                                             b. horizontal

4. Are streams in this area downcutting or laterally eroding?

a. downcutting                                                   b. laterally eroding

5. In which stage of the cycle of stream erosion is this area?

a. old age                            b. mature                      c. youthful

Map 5.2 is the southeast portion of the map above, magnified to show Grape Creek. Use this map to answer question 6.

6. Calculate the stream gradient of Grape Creek in ft/mile. Use the index contour just above the “m” in Temple Canyon for your initial spot. Measure the gradient to the index contour past the word Creek (the last contour before it reaches Arkansas River). The distance between these areas is ~1.6 miles (measured along the curving distance of the non-magnified stream). What is the gradient?

a. 15’/mile                         b. 100’/mile                         c. 125’/mile                         d. 200’/mile

Use the Omaha North, Nebraska-Iowa Map 5.3 on the next page to answer questions 7-11.

7. Observe the stream on the Omaha N, Nebraska-Iowa quadrangle. In which stage of the cycle of stream erosion is this area?

a. old age                         b. mature                             c. youthful

8. Compare the contour intervals from the Royal Gorge, Colorado map (map 5.1) to the Omaha N, Nebraska-Iowa map. Would you expect the gradient of the Missouri River in Nebraska to be greater or less than the gradient that you calculated for the Grape River in Colorado?

a. less than the Grape River gradient                              b. greater than the Grape River gradient

9. Locate the state boundary between Nebraska and Iowa along the Missouri River. Why does the boundary depart from the river channel?

a. When the boundary was created, Iowans wanted the Carter Lake area in their state.

b. The boundary follows the course of the river at the time that it was drawn; the river has since moved.

c. None of the above

10. What is the term for the geologic feature called Carter Lake?

a. entrenched meander                         b. oxbow lake                         c. cutbank                         d. point bar

11. Was Carter Lake cut off before or after the state boundary between Nebraska and Iowa was drawn?

a. before                                             b. after