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The oldest scientific society in the Rocky Mountain region

Founded in 1882, the Colorado Scientific Society promotes knowledge, the understanding of science, and its application to human needs, focusing primarily on earth science, but welcoming members with interests in all fields of science.  Learn more.

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March Meeting – Thursday, March 16, 2017

The Far-Reaching Effects of Wastewater Injection: Recent Case Studies of Anthropogenic Earthquakes

Will Yeck, National Earthquake Information Center, USGS

Shepherd of the Hills Presbyterian Church, 11500 W. 20th Ave., Lakewood CO
Social time beginning at 6:30; meeting & program at 7:00
Map for Shepherd of the Hills


February Meeting – Thursday, Feb. 16, 2017

Landscape Evolution of Colorado

Late Neogene Tectonic and Volcanic Fragmentation and Middle Pleistocene Climate-Driven Drainage Integration of the Southern Rocky Mountains

Cal Ruleman, Geology and Environmental Change, USGS

Synopsis: The southern Rocky Mountains have long been a focus for lithologic, structural, and geomorphic studies. Building on this previous work using newly developed geomorphic, chronologic, geodetic, geophysical, and pedologic analyses, I am developing a unified model to: (1) explain the timing and mechanism for regional middle Pleistocene incision; (2) determine regional correlations; and, (3) resolve discrepancies between bedrock and surficial geologists. I will highlight recent work on diamictons and Quaternary deposits in the San Luis Valley, Sawatch Range, and upper Arkansas valley. Through this work I have developed the following geomorphic sequence: (1) deposition of extensive Rocky Flats-correlative alluvium on adjacent Rocky Mountain piedmonts and continued tectonically-induced aggradation within Rio Grande rift basins (>640 ka); (2) eruption of the Lava Creek B tephra at ~640 ka; (3) subtle landscape dissection and deposition of inset Verdos-correlative alluvium (~621-478 ka); (4) San Luis basin spillover and integration into Rio Grande and widespread deposition of diamicton on Poncha Pass and around the perimeter of high altitude mountains (478-374 ka); and, (5) intermountain deep-canyon incision and adjacent Front Range and San Juan Basin piedmont incision and widespread deposition of Slocum-correlative alluvium on flanking piedmonts (~374-191 ka). All younger deposits and landforms are deeply inset into the topography and easily distinguishable.

Full Abstract: The southern Rocky Mountains have long been a focus for lithologic, structural, and geomorphic studies. Building on this previous work using newly developed geomorphic, chronologic, geodetic, geophysical, and pedologic analyses, I am developing a unified model to explain the timing and mechanism for regional middle Pleistocene incision, determine regional correlations, and resolve discrepancies between bedrock and surficial geologists. Recent work within the San Luis Valley, Sawatch Range, and upper Arkansas Valley demonstrate a linkage between the Lake Alamosa highstand ~385 ka, maximum basin fill elevation, and deposition of the first Pleistocene diamicton above generally finer-grained deposits of the Santa Fe Group and Dry Union Formation. These boulder diamictons have been previously mapped around the region as QTd or Tg (Quaternary-Tertiary diamicton or Tertiary gravel) depending on the breadth of geologic time the author was familiar with and focusing on.  They were also generally interpreted to be the result of rapid tectonic uplift.  The presence of ~640 ka Lava Creek B ash in the underlying, lower-energy deposits of the Santa Fe Group provides a maximum age for the diamicton and indicates a <640ka dramatic change in the basin-fill sedimentology leading to deposition of coarse axial gravels linking previously closed, and disconnected intermountain basins adjacent to the high elevations. We interpret these sedimentologic and geomorphic relationships to indicate the regional onset of major middle Pleistocene glacial episodes younger than MIS 16, ~676-621 ka. Within the San Luis Valley, maximum aggradation elevation, basin integration processes, and incision into the Rio Grande gorge occurred even later, <420 ka (MIS 12), coeval to placement of the first diamicton on Poncha Pass. Poncha Pass is where intermountain tectonically-fragmented basin stratigraphy meets the Front Range piedmont Pleistocene stratigraphy along the Arkansas River and through the Royal Gorge. Regional geologic mapping and topographic correlations demonstrate that similar relationships (i.e., coarse bouldery deposits with a silty clay matrix capping interfluves and overlying/pre-dating deeply incised topography) exist in the Aspen region and across South Park, along the Black Canyon of the Gunnison and Eagle River, and potentially adjacent to any region above 3600 m (~12,000 feet).
The geomorphic sequence is as follows: 1) deposition of extensive Rocky Flats-correlative alluvium on adjacent Rocky Mountain piedmonts and continued tectonically-induced aggradation within Rio Grande rift basins (>640 ka)(>MIS 16); 2) eruption of the Lava Creek B tephra from the Yellowstone caldera complex ~640 ka; 3) subtle landscape dissection and deposition of inset Verdos-correlative alluvium containing Lava Creek B ash on piedmonts (i.e., Front Range/Denver , San Juan, Wind River, and Bighorn Basins)(~MIS 15-13, ~621-478 ka; 4) San Luis basin spillover and integration into Rio Grande and widespread deposition of diamicton on Poncha Pass and around the perimeter of high altitude mountains (MIS 12-11, 478-374 ka); 5) intermountain deep-canyon incision and adjacent Front Range and San Juan Basin piedmont incision and widespread deposition of Slocum-correlative alluvium on flanking piedmonts (MIS 11-7, ~374-191 ka). All younger deposits and landforms are deeply inset into the topography and easily distinguishable. Coeval to glacially-induced middle Pleistocene Southern Rockies incision, Great Plains neotectonics and the evolution of the Arkansas River-Sand Creek-South Platte fluvial system can be directly related to the timing of Laurentide “Kansan” glaciation, the southernmost and most expansive Laurentide icesheet during the Pleistocene. Tentative correlations suggest that Front Range Bear and Clear Creek drainages have the same geomorphic sequence, explaining peculiar deposits and geomorphic relations between Green and North and South Table Mountains and the Continental Divide.

Biography:  Cal Ruleman studied geology at the University of Montana and Montana State University and has been performing geological investigations for the last twenty years in various tectonic and geomorphic settings including Montana, Idaho, Wyoming, Nevada, Colorado, New Mexico, Alaska, Suriname, South America, Afghanistan, and Nepal. He joined the U.S. Geological Survey in 2007. His work has ranged from Archean to Holocene with a focus on geomorphology and landscape evolution. In addition to geologic mapping, paleoseismology, and geomorphic analyses, he employs various Quaternary relative and absolute dating techniques including pedology, 3He-, 10Be-, and 26Al-surface exposure dating, and U-Th soil carbonate dating techniques to resolve geologic problems. His geologic mapping and investigations within the Rocky Mountains from western Montana to northern New Mexico address: 1) temporal and spatial migration of intermountain neotectonics, 2) the timing and process of gorge formation and deep incision below glaciated regions, 3) timing of Last Glacial Maximum ~22 ka and rates of deglaciation, 4) timing of onset and sequence of major Pleistocene glaciations of North America, and 5) bedrock structural development of the region over multiple tectonic episodes. Building upon the lithologic, structural, and geomorphic findings of our predecessors, he combines newly developed geomorphic, chronologic, geodetic, paleoseismologic, geophysical, and pedologic analyses to develop unified models explaining the timing and mechanism for regional middle Pleistocene incision, quantifying geomorphic processes, determining regional correlations, and attempting to resolve discrepancies between traditional bedrock and surficial geologists.


Shepherd of the Hills Presbyterian Church, 11500 W. 20th Ave., Lakewood CO
Social time beginning at 6:30; meeting & program at 7:00
Map for Shepherd of the Hills


Future Colorado Scientific Society Meetings

Abstracts of past Colo. Scientific Society meetings

Read the February 2017 newsletter.


The Colorado Scientific Society was founded in 1882 as a forum for the exchange of observations and ideas on the topics of earth science. Our lecture series occurs on the third Thursday of each month, from September through May. Lecture topics largely focus on earth science, and are open to the public. In addition to our monthly lecture series, the society is also active in public service. We fund student research grants, construct and post signs that describe local geologic features, and organize and lead several field trips.