STATUS OF PHOTOGEOLOGY IN THE U. S. GEOLOGICAL SURVEY 
By 
* 
Richard G, Ray 
U. S. Geological Survey 
| should like to talk about photogeology in the U. S. Geological Survey 
in reference to operations, research, and training primarily by personnel of the 
Photogeology Section. But first, perhaps it would be appropriate to define the 
term "photogeology", Despite the increasing use of aerial photographs in geo- 
logic study over the past few decades, it was not, to my knowledge, until 1941 
that a definition of the term "photogeology" appeared in the literature. 
H. C. Rea then defined photogeology merely as " geologic interpretation of 
aerial photographs", | would like to emphasize the word "geologic" in his defi- 
nition to contrast geologic interpretation of photographs with the many other types 
of photointerpretation. | would hasten to add, however, that our present feeling 
would carry a definition of photogeology a bit further, Just as completion of a 
geologic map is normally a part of field geologic study, so too is the completion of 
a photogeologic map normally a part of photogeologic study, This implies that 
certain methods of compilation, as well as techniques of measuring such data as 
strikes and dips of beds, displacements of faults, thicknesses of strata, etc., are 
a necessary part of a definition of photogeology. |n other words it may be said 
that photogeology basically involves I) interpreting, 2) measuring, and 3) com- 
piling. 
Operations 
With this as a background let us now consider photogeologic work in the 
Photogeology Section. Most of the current work is devoted to operations. This 
photogeologic work involves 14 geologists working on numerous projects at the 
three main headquarters of Geological Survey activity: Washington, D. C.; 
Denver, Colorado; and Menlo Park, California. The variety of projects, including 
stratigraphic and structural studies of areas of well-exposed to poorly exposed rocks, 
studies of structure in heavily forested igneous-metamorphic terrane, studies of 
specific mine areas and dam sites, as well as compilation of isopachous maps, may 
give some idea of progress In the geologic Interpretation field when one considers 
that almost all photogeologic effort of a few years back was directed toward studies 
of sedimentary terrane for petroleum purposes, and only terrane that was gently 
folded or only slightly disturbed. 
  
* Publication authorized by the Director, U. S. Geological Survey