8. Annotation of aerial photographs 
9, Recognition of geologic features 
10. Interpretation of geologic features 
To demonstrate the various techniques in using aerial pho- 
tographs for geologic mapping, the Maverick Springs, Wyoming, 
area was selected. Topographic maps at a scale of 1:24,000 
and with a 20-foot contour interval are available. Also a 
geologic map of the area prepared by standard field methods has 
been published.,1/ Aerial photographs of the Maverick Springs 
area are at the approximate scale of 1:24,000 and are the same 
photographs used for the multiplex compilation of the topo- 
graphic map. 
Within the area sedimentary rock units are well exposed 
on the flanks of anticlines and synclines, and several faults 
are present. In addition to these structural features there 
are numerous examples of geomorphic features such as the dis- 
sected remnant of an old erosion surface and various stream 
patterns. With these photographs the trainee is able to make 
observations and interpretations of the geology and compare his 
findings with those shown on the published geologic map. The 
photographs are also used in the performance of many of the 
exercises and problems using the photogrammetric equipment. 
In the training classes geometry of the photographs is 
first studied. Definitions of the principal point, isocenter, 
nadir, pass points, fiducial marks, focal length, photo base, 
and scale are given, Methods of proper orientation of vertical 
photographs for stereoscopic examination are demonstrated. The 
various stereoscopes in use by the U. S. Geological Survey are 
described and examined. The trainees are given a simple test 
to determine their ability to see stereoscopically. 
1/ U. S. Geological Survey Oll and Gas Investigations Preliminary 
Map 13. Geologic and structure contour map of the Maverick 
Springsarea, Fremont County, Wyoming, by D. Andrews, 1944,