The primary methods used for geologic mapping of the MCQ were to utilize aerial photographs and intensive field checks to verify map units. The air photos were used as stereo pairs to enhance their utility for identifying stratigraphic units and faults of the Balcones Fault Zone. The photos were taken in 1958 and are at a scale of about [TBD]. The photo images were downloaded from the USGS Earth Explorer website, where they are free to the public.
A major advantage of the 1958 photos is that they were taken just two years after a major drought in Texas that had lasted for about seven years and ended in 1956. The vegetation had been curtailed during the drought, exposing the bedrock units and faults, and had not recovered substantially before the 1958 photos were taken. Often the air photo mapping was done in advance and verified or changed as needed during field visits and outcrop checks. The mapping was transferred from the photos to the topographic base map using clear transparency sheets printed from the base map and overlaid on the photos at the same scale.
[In preparation]