morphology   (topographic   features   produced   by erosion). The use of aerial photographs to show and identify soils is based upon your ability to recognize typical patterns formed under similar conditions. An example might be soil profile and weathering. Principal elements that can be identified on a photograph and that provide a trained observer with clues to the identification of soils are  landform,  slopes,  drainage  patterns,  erosional characteristics,  soil  color  or  “tone,”  vegetation,  and  land use. The form or cofiguration of the land in different types of deposits is definitely characteristic and can be identified on aerial photographs; for example, in desert areas, characteristic dune shapes indicate areas covered by sand subject to movement by wind. Prevailing ground slopes are clues as to the texture of  the  soil.  Steep  slopes  are  characteristic  of  granular materials,  while  relatively  flat  and  smoothly  rounded slopes may indicate more plastic soils. The absence of surface drainage or a very simple drainage pattern often indicates pervious soil. A highly integrated drainage pattern often indicates impervious soils that are plastic and usually lose strength when wet. Drainage  patterns  tend  to  reflect  underlying  rock structure. The pattern of erosion often provides clues as to the character of the soil. For instance, the cross section or shape of a gully is controlled mainly by the cohesiveness of  the  soil.  Each  abrupt  change  in  grade,  direction,  or cross section indicates a change in the soil profile or rock layers.  Short,  V-shaped  gullies  with  steep  gradients  are typical  of  noncohesive  soils;  U-shaped  gullies  with steep gradients indicate deep, uniform silt deposits. Cohesive  soils  generally  develop  round,  saucer-shaped gullies. The color of soil is shown on aerial photographs by shades of gray; they range from almost white to almost black.  Soft,  light  colors  or  tones  generally  indicate pervious, well-drained soils. Large, flat areas of sand are frequently indicated by uniform, light gray color tones, a  flat  appearance,  and  a  lack  of  conformity;  this indicates  a  natural  surface  drainage.  Clays  and  organic soils frequently appear as dark gray to black areas. In general, a sharp change in color tones represents a change in soil texture. The character of the vegetation may reflect the surface  soil  type;  however,  its  significance  is  often difficult to interpret because of the effects of climate and other  factors.  To  those  with  local  experience,  both cultivated  and  natural  vegetation  cover  are  good indicators of soil type. Knowing the use to which agricultural land is put is often  helpful  in  soil  identification.  For  example, orchards  require  well-draining  soils;  therefore,  the presence of an orchard implies a sandy soil. FIELD  OBSERVATIONS Through the use of the various types of published information and aerial photographs, the exploration of a general area maybe narrowed down to several smaller areas  suitable  for  further  investigation.  The  extent  and method of collecting more detailed information by field observations  depends  on  the  time  available. Rapid  ground  observation  along  the  proposed highway   or   airfield   location   may   yield   valuable information when conditions do not permit you to make a  complete  or  deliberate  soil  survey.  Observe  the  soil profile along the natural banks of streams, eroded areas, bomb craters, road cuts, or other places where you see stratified areas. Such observations may indicate types of soil and depths of layers. Scrape off loose surface soils before  you  examine  and  make  field  identification. Samples  may  be  taken  from  exposed  soils  for  testing  in a  field  laboratory;  however,  sampling  and  testing  are normally at a minimum in this type of soil survey. Surface soils may be exposed by the use of pick and shovel, particularly in areas of questionable soils or at critical points in the location. Soils identified in the hasty survey may be located by field sketches or on available maps  or  photographs. METHODS  FOR  COLLECTING SAMPLES A deliberate investigation is made when time and equipment are available and when a more thorough investigation  of  the  subsoil  is  needed  than  can  be obtained by hasty field observations. The two most commonly  used  methods  of  obtaining  soil  samples for deliberate investigations are test pits and test holes. A test pit is an open excavation that is large enough for a man to enter and study the soil in its undisturbed condition.  This  method  provides  the  most  satisfactory means for observing the natural condition of the soil and the collection of undisturbed samples. The test pit is usually dug by hand; however, power excavation by 16-8