Geography 360
GEOMORPHOLOGY
SPRING 2006
Name _________________Soil maps are an important tool to use along with topographic maps, geologic maps, and other types of maps, as well as air photos and satellite images that can help with interpretation of the landscape. Variations in soils often reflect variations in the land surface. Clues to the types of landforms, the relief (slope and aspect), the relative ages of the different land surfaces, the types of geomorphic processes that are active or were active in the past, microclimates, variations in vegetation, and sources of parent material, may all be reflected in varying degrees in soils maps.
The object of this exercise is to familiarize you with basic soil formation characteristics and terminology, as well as the information resources available to you through the Soil Conservation Service in (almost) every county in the U.S.
In this exercise, you will read through the introductory pages of the "Soil Survey of Sonoma County", pages 1-2 (provided herewith as a handout), and also look at the section on pages 170-175. Then, I would like you to look through the book, to see what types of information are included and how they are organized. See the instructions on the inside front cover and first page, then browse through, looking at examples of these sections of the book.
After you have become somewhat familiar with the organization and information in the SCS Sonoma County booklet, I would like you to choose a Section (in the Township and Range system) on one of the 7.5' quads and air photo sets we've put out. Choose an area that has as much variation in topography and landform types as possible. Please check with me regarding your choice before you begin working. Look at the large format air photos that correspond with the map and the geologic map of the region, as well.
Then find your chosen area on the general soils map for the County (in the middle of the SCS book). Turn to the specific map for your Section, and make a list of Map Units for soils on that section. Then turn to the Index of soil map units to find the descriptions for each soil unit. Read both the Association descriptions, beginning on page 3, and the detailed Series descriptions of the soils map units, beginning on page 9. In this section you will find profile descriptions of the soil series that appear on your section of the map. The descriptions should include information on parent material of the soil, climate, depth of soil development, and topography of the surface. You'll notice that a single soil name is commonly divided into separate units simply by slope. You can lump all of those with the same name together, regardless of degrees of slope.
You should also look up other types of information on your soils in the Sonoma County Soils book, such as engineering properties, capability units, woodland or range group, wildlife group, etc.
Make a photocopy enlargement of your map section and soils map section. (There are copy machines in Schultz Library.) Then write a brief description of the following and modify your photocopy of the soils map to illustrate your description:
1. Identify as many as you can of the dominant landforms and geomorphic processes active in your section (e.g. floodplain, alluvial fan, bedrock outcrop, mass movements), and discuss the differences in soil types identified on these landforms. Ask for help in identifying landforms if you need to. You may use colored pencils to lightly color in each of the different soil types on your photocopy of the soils map.
2. Then on the topo map, draw bold boundaries around general landform types you see. Make a map key of colors or boundary lines on your maps, so that I know what you're referring to. In your written analysis, be sure to include climate, slope, aspect (where relevant), parent material, and other soil features that seem to characterize your particular landforms, from the descriptions. Also include vegetation cover or land use, if you can tell from the maps and photos. Keep in mind the dates the maps and photos (and Soil Survey) were made. Think about the differences in thickness of the soils, what they are composed of, and how long they've been forming (how well developed they are). Do you see any relationship between types of soils and the other land surface characteristics you've identified?
This is a Very Loose Exercise -- Do not stress over "Doing It Right." Rather, take some time to become familiar with soils in relation to landforms. We will follow up on this in subsequent field trips.
Because there are only limited sets of SCS Soil Survey books, I encourage you to work in groups. I expect this will take some cooperation, organization, and time, so I've given you two weeks to finish it. Please, take advantage of this time -- don't wait until the last minute to work on it. Next week we are taking a field trip, so there will be no extra lab time during class to work on this. Your Field Trip Notes will constitute Lab 3, also due on Feb. 23. However, Lab 3 will be done completely in the field, so it should take no out-of-class time.
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copyright D.E.Freidel, 2000 No portion of this document may be copied without written permission of the author.