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Posted 4/3/2018

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By Dena O'Dell
U.S. Army Corps of Engineers Los Angeles District


LAS VEGAS – Spread out across more than 195,000 acres of the Mojave Desert, Red Rock Canyon National Conservation Area is a geologist’s playground.

With its picturesque canyons displaying an array of colors, rock formations and unique features molded over more than 600 million years, to preserved archeological discoveries, like pictographs and petroglyphs etched and drawn on canyon walls from cultures long ago, the secrets Red Rock Canyon holds can tell scientists a story that may save lives in the future.

For about 30 U.S. Army Corps of Engineers’ geologists and technicians, a March 15 visit to Red Rock Canyon provided the perfect setting to study ancient earthquakes and floods in hopes of preparing critical infrastructure, like dams and levees, for potential future flooding and seismic events.

During the visit, the geologists participated in an exercise that focused on finding clues from pre-historic and historic floods that once poured from the mountains, through the canyon and out into the Las Vegas valley.

Collecting information about the size and timing of prehistoric floods helps improve the protection that dams and levees are designed to provide, according to Keith Kelson, engineering geologist with the Corps’ Sacramento District. Throughout the U.S., much of the critical infrastructure, including bridges, power plants, dams, levees, housing tracts, environmental habitats, cultural resource sites and other societally important features border or cross rivers. The goal of these “paleoflood” analyses is to develop data on the timing and magnitude of large, infrequent floods and improve long-term flow frequency statistics, he said.

“This information gives hydrologists and risk analysts a better handle on the likelihood of large floods,” Kelson said, “which is an important part of assessing dams and levee safety across the country.”

Observing some of the canyons’ archeological and geological features gave the group a better understanding of determining the size and locations of past floods in the area.

“One of the things some participants found most fascinating was the ways of evaluating large floods by using many different disciplines, not just geology and hydrology, but also archeology and cultural history,” Kelson said. “We discussed the use of archeological pictographs for figuring out a height limit on the size of past floods. Clay imprints on the canyon walls suggest the water hasn’t risen to those heights in hundreds, or perhaps, thousands of years.”

In terms of the Corps’ Los Angeles District area, which includes southern California, Arizona and portions of Nevada and Utah, many dams and levees are undergoing safety evaluations or will be in the near future, he said.

Flash floods are relatively common in desert environments, and the arid setting is good for producing and preserving geologic deposits from floods. It also is well suited for conducting paleoflood analyses, he added.

“Our arid environment is a wonderful recording device that, with the right tools, can be deciphered to tell us (a lot of) useful information about the timing and size of past floods,” he said. “The principles and concepts of paleoflood analyses can be readily applied to many of the dams and levees in the Los Angeles District, including those in populated areas, like the Los Angeles Basin.”

The Corps is planning to start a paleoflood analysis for a dam in Orange County, Kelson said, with the goal of telling more about the potential for rare floods.

“Similar analyses could be conducted for evaluating flood loading for the many important levee systems that protect large populations in Los Angeles and Orange counties,” he said.

The geological tour of Red Rock Canyon also included a hike along the Keystone Thrust Fault, led by Doug Bliss, chief of the Geotechnical and Engineering Services Branch, Regional Geotechnical Center, with the Corps’ Alaska District.

The fault, one of the most significant geological features of Red Rock Canyon, developed more than 65 million years ago, when a fracture in the earth's crust drove one crustal plate over the top of another. At Red Rock Canyon, this resulted in the oldest rocks – gray carbonate rocks from what was previously an ocean floor – being thrust over the younger tan and red sandstone.

James Farley, chief of the Geotechnical Branch with the Corps’ Los Angeles District, said the geology exercise at Red Rock Canyon showcased the “very interesting and significant Keystone Thrust Fault and geologic formations within Red Rock Canyon,” and the paleoflood lesson showed participants field conditions to identify past flood events and how it may be used to improve hydrologic loading estimates.

“The exposed geologic features were fascinating, and the instruction on Corps’ paleoflood analyses educated us on the ongoing improvements to understand hydrologic loading,” he said.

PART OF A BIGGER PICTURE

The visit to Red Rock Canyon was one of two capstone field trips that concluded the 2018 Geotechnical, Geology and Materials Community of Practice National Training Event March 13 to 15 in Boulder City.

About 105 Corps’ geotechnical engineers, geologists, materials laboratory technicians and subsurface exploration drillers from across the nation attended the training event, where they discussed everything from tools of the trade to methods, techniques and lessons learned from projects throughout the U.S.

Marc Goodhue, senior regional civil engineer with the Corps’ South Pacific Division,  who helped coordinate logistics for the event and also provided a presentation during the training, said it brought together a large number of very talented and knowledgeable people in the Corps’ geotechnical and geology fields.

“Bringing this group together from across all of the divisions provides an excellent opportunity for us to teach each other,” he said. “I am positive that everyone who attended gained some new knowledge, and hopefully, a new point of contact they can use if they need help in the future.”

Kelson, who in addition to leading the field trip at Red Rock Canyon, also taught a paleoflood analysis class during the three-day workshop, said it provided an excellent venue for learning the various technical capabilities and special expertise within the Corps, as well as allowed for a valuable exchange of information among a range of Corps’ personnel.

“The workshop gave participants a window into the diversity of expertise, experience and skill sets within the organization,” he said, “and helped build bonds for collaborating on future civil works and military projects.”

2018 Geotechnical Bureau of Land Management dam and levee safety geology Geology and Materials Community of Practice National Training Event geotechnical engineering paeloflood hydrology Red Rock Canyon National Conservation Area U.S. Army Corps of Engineers Headquarters