This is a scanned version of the text of the original Soil Survey report of Yamhill County, Oregon, issued January 1974. Original tables and maps were deleted. There may be references in the text that refer to a table that is not in this document. Updated tables were generated from the NRCS National Soil Information System (NASIS). The soil map data has been digitized and may include some updated information. These are available from http://soildatamart.nrcs.usda.gov. Please contact the State Soil Scientist, Natural Resources Conservation Service (formerly Soil Conservation Service) for additional information. SOIL SURVEY OF THE YAMHILL AREA, OREGON BY GEORGE E. OTTE, DUANE K. SETNESS, WALTER A. ANDERSON, FRED J. HERBERT, JR., AND CLARENCE A. KNEZEVICH, SOIL CONSERVATION SERVICE UNITED STATES DEPARTMENT OF AGRICULTURE, SOIL CONSERVATION SERVICE, IN COOPERATION WITH THE OREGON AGRICULTURAL EXPERIMENT STATION THE YAMHILL AREA consists of all of Yamhill County, except In mapping the survey area, two intensities of soil mapping for the extreme western part that is in the Siuslaw National Forest. were used. In the forested-hilly or mountainous part of the survey It is located on the west side of the lower middle part of the area, soils were examined at moderate to wide intervals and were Willamette Valley (fig. 1) and is bounded by Washington, mapped at medium intensity. In the smooth Willamette Valley part, Clackamas, Polk, the soils were examined at close intervals and were mapped at high intensity, or in considerably more detail than in the forested-hilly or mountainous part. Most of the soils mapped at high intensity have a narrow range of slope. They are in the southern and eastern parts of the survey area, and the soils mapped at medium intensity are in the western and northern parts. To show which soils were mapped at medium intensity and which at high intensity, the kind of map symbol assigned to the soils mapped at medium intensity was made to differ slightly from the one assigned to the soils mapped at high intensity. The second letter of the map symbol is a capital letter if the mapping unit is one of those mapped at medium intensity, for example, ASE. It is a small letter if the mapping unit is one of those mapped it high intensity, for example, CaB. A list of all the soils in the survey area, their map symbol, and the capability unit, woodland group, and wildlife group to which each has been assigned can be found in the "Guide to Mapping Units" at the back of this publication. How This Survey Was Made Soil scientists made this survey to learn what kinds of soil are in the Yamhill Area, where they are located, and how they can be used. The soil scientists went into the Area knowing they likely Figure 1.-Location of the Yamhill Area in Oregon. would find many soils they had already seen and perhaps some they had not. They observed the steepness, length, and shape of and Tillamook Counties. The Willamette River is the eastern slopes, the size and speed of streams, the kinds of native plants or boundary. The Yamhill Area extends from about 15 miles crops, the kinds of rock, and many facts about the soils. They dug southwest of Portland to within 11 miles of the Pacific Ocean. many holes to expose soil profiles. A profile is the sequence of McMinnville, the county seat and largest town, is in the natural layers, or horizons, in a soil; it extends from the surface east-central part. The total land area is approximately 424,360 down into the parent material that has not been changed much by acres. About 386,380 acres is privately owned, and most of the leaching or by the action of plant roots. remaining 37,980 acres is managed by the U.S. Bureau of Land The soil scientists made comparisons among the profiles they Management. studied, and they compared these profiles with those in counties The survey area is divided into two general areas: a smooth nearby and in places more distant. They classified and named the valley area in the southern and eastern parts that is used for soils according to nationwide, uniform procedures. The soil series farming, and a hilly or mountainous area in the western and and the soil phase northern parts that is used for timber. With the exception of a few small streams and the Nestucca River, which originate near the summit of the Coast Range and flow westward to the Pacific Ocean, the drainage of more than 95 percent of the Area is eastward through the forks of the Yamhill River and Chehalem Creek into the Willamette River which flows into the Columbia River at Portland. are the categories of soil classification most used in a local records and from field or plot experiments on the same kinds of survey. soil. Yields under defined management are estimated for all the Soils that have profiles almost alike make up a soil series. soils. Except for different texture in the surface layer, all the soils of one But only part of a soil survey is done when the soils have been series have major horizons that are similar in thickness, named, described, and delineated on the map, and the laboratory arrangement, and other important characteristics. Each soil series data and yield data have been assembled. The mass of detailed is named for a town or other geographic feature near the place information then needs to be organized in such a way as to be where a soil of that series was first observed and mapped. readily useful to different groups of users, among them farmers, Chehalis and Jory, for example, are the names of two soil series. All the soils in the United States having the same series name are managers of woodland and rangeland, and engineers. essentially alike in those characteristics that affect their behavior On the basis of yield and practice tables and other data, the soil in the undisturbed landscape. scientists set up trial groups. They test these groups by further Soils of one series can differ in texture of the surface soil and in study and by consultation with farmers, agronomists, engineers, slope, stoniness, or some other characteristic that affects use of and others, then adjust the groups according to the results of the soils by man. On the basis of such differences, a soil series is their studies and consultation. Thus, the groups that are finally divided into phases. The name of a soil phase indicates a feature evolved reflect up-to-date knowledge, of the soils and their be- that affects management. For example, Jory clay loam, 2 to 7 havior under present methods of use and management. percent slopes, is one of several phases within the Jory series. After a guide for classifying and naming the soils had been worked out, the, soil scientists drew the boundaries of the individual soils on aerial photographs. These photographs show woodlands, buildings, field borders, trees, and other details that help in drawing boundaries accurately. The soil map in the back of General Soil Map this publication was prepared from the, aerial photographs. The general soil map at the back of this survey shows, in color, The areas shown on a soil map are called mapping units. On the soil associations in the Yamhill Area. A soil association is a most maps detailed enough to be useful in planning the landscape that has a distinctive proportional pattern of soils. It management of farms and fields, a mapping unit is nearly normally consists of one or more major soils and at least one equivalent to a soil phase. It is not exactly equivalent, because it, minor soil, and it is named for the major soils. The soils in one is not practical to show on such a map all the small, scattered bits association may occur in another, but in a different pattern. of soil of some other kind that have been seen within an area that A map showing soil associations is useful to people who want is dominantly of a recognized soil phase. a general idea of the soils in an area, who want to compare Some mapping units are made up of soils of different series, or different parts of an area, or who want to know the location of of different phases within one series. One such kind of mapping large tracts that are suitable for a certain kind of land use. Such a unit, called an undifferentiated group, is shown on the soil map of map is a useful general guide in managing a watershed, a wooded the Yamhill Area. tract, or a wildlife area, or in planning engineering works, recre- An undifferentiated group is made up of two or more soils that ational facilities, and community developments. It is not a suitable could be delineated individually but are shown as one unit map for planning the management of a farm or field, or for because, for the purpose of the soil survey, there is little value in selecting the exact location of a road, building, or similar separating them. The pattern and proportion of soils are not structure, because the soils in any one association ordinarily uniform. An area shown on the map may be made up of only one differ in slope, depth, stoniness, drainage, and other of the dominant soils, or of two or more. The name of an characteristics that affect their management. undifferentiated group consists of the names of the dominant The soil associations in the Yamhill Area are each discussed in soils, joined by "and." Kilchis and Klickitat soils, 60 to 90 percent the following pages.