[NOTE: This page is being replaced. Please go here.]
The geology of the MCQ includes the description of the geologic characteristics and how they are distributed over the area encompassed. The geologic map complements the description – stratigraphy, structural geology, etc. – by depicting how these characteristics are expressed within the quadrangle. As noted, the Mountain City topographic quadrangle serves as the base map on which the geological information is superimposed.
The geologic mapping of the MCQ for this website is intended to represent the “next generation“ of detailed mapping at a scale of 1:24,000. Portions of the area have been mapped previously by Grimshaw, 1976 (dissertation map); The UT Bureau of Economic Geology, 1976 (Report of Investigation #86), Smith, 1978 (thesis map) and Kolb, 1981 (thesis map). This next generation is based on better aerial photographs (taken in 1958 at a scale of [TBD]) than were used previously and on enhanced understanding of fault patterns of the Balcones Fault Zone.
The geologic mapping has been done on nine segments of the quadrangle base map. The segments are 2-1/2 minute areas of the 7-1/2 minute quadrangle, which conveniently fit on 8-1/2 x 11 paper at full scale. The geologic mapping also extends into adjacent quadrangles by varying amounts, so these adjacent segments are also included. The map segments are presented on this webpage according to the diagram shown below. The MCQ segments are shaded.
Each Tier consists of five segments that are numbered 1 to 5 from west to east. Tier 1 includes the lower 1/3 of the Signal Hill Quad above (north of) the MCQ. Tiers 2, 3 and 4 each include the three MCQ segments and a segment on the west (Dripping Springs Quad) and on the east (Buda Quad). Tier 5 covers the upper 1/3 of the San Marcos North Quad and segments of adjoining quads (Hunter and Uhland). This geologic mapping coverage is included in the companion SMNQ website.
When the geologic mapping on the segments had reached about 80-90% completion, a memorandum was submitted to Brian Hunt of the Barton Springs Edwards Aquifer on October 14, 2018. The mapping has continued afterward, particularly in Tier 4. The strategy in posting the mapped segments here is to start with the October 14 version and replace the segment with more up-to-date versions as improvements are made.
Tier 1
This tier covers the quadrangle north of the MCQ, which is the Signal Hill Quad. Segments 1-1 and 1-5 are not included because they are not as relevant to the MCQ mapping. Tier 1 was mapped by Kolb (1981, lower 1/3 of the map) and is being re-mapped for MCQ project. Kolb’s map can be viewed here.
Tier 1, Segment 1. Not used.
Tier 1, Segment 2 (In preparation). Update of Kolb, 1981.
Tier 1, Segment 3 (In preparation). Update of Kolb, 1981.
Tier 1, Segment 4. Update of Kolb, 1981.
Tier 1, Segment 5. Not used.
Tier 2
Tier 2 covers the upper 1/3 of the MCQ and segments to the west (Driftwood Quad) and east (Buda Quad). Tier 2, Segment 1 was mapped previously by Ed Collins [TBD]. Collins’ mapping may be viewed here. The Buda Quad has not previously been mapped at the 7-1/2 minute scale.
Tier 2 Segment 1 (In preparation). Collins, 2002.
Tier 2, Segment 2
Tier 2, Segment 3
Tier 2, Segment 4
Tier 2, Segment 5. Buda Quad
Tier 3
Tier 3 covers the middle 1/3 of the MCQ and segments to the west (Driftwood Quad) and east (Buda Quad). Tier 3, Segment 1 was mapped previously by Ed Collins, 2002. Collins’ mapping may be viewed here. The Buda Quad has not previously been mapped at the 7-1/2 minute scale.
Tier 3, Segment 1 (In preparation). Collins, 2002.
Tier 3, Segment 2
Tier 3, Segment 3
Tier 3, Segment 4
Tier 3, Segment 5. Buda Quad
Tier 4
Tier 4 covers the lower 1/3 of the MCQ and segments to the west (Driftwood Quad) and east (Buda Quad). Tier 4, Segment 1 was mapped previously by Ed Collins, 2002. Collins’ mapping may be viewed here. The Buda Quad has not previously been mapped at the 7-1/2 minute scale.
Tier 4, Segment 1 (In preparation). Collins, 2002.
Tier 4, Segment 2
Tier 4, Segment 3
Tier 4, Segment 4
Tier 4, Segment 5. Buda Quad. Not Used.
Tier 5
As noted above, Tier 5 includes the upper 1/3 of the San Marcos North Quad. it is therefore included in the SMNQ website rather than here.