View looking southwest from Sugarloaf along Interior Valley to Inner Basin. Treeless peaks at the southwest end of the basin are Fremont (left) and Agassiz (right). Light green aspen trees in Interior Valley are on terminal moraines up to 240 feet high.Â
View looking southwest from O’Leary Peak to San Francisco Mountain.
Author courtesy
Rock outcrop in Inner Basin at the base of Humphreys Peak that was polished and striated by a glacier.Â
Author courtesy
View looking southwest from Sugarloaf along Interior Valley to Inner Basin. Treeless peaks at the southwest end of the basin are Fremont (left) and Agassiz (right). Light green aspen trees in Interior Valley are on terminal moraines up to 240 feet high.Â
The Pleistocene Epoch, approximately 11,700 to 2.6 million years ago, is known as the Ice Age. Multiple times during this period much of Earth’s land surface was covered by thick sheets of ice. In places where ice was thick enough to flow under its own weight, it became a glacier and flowed away from areas of greatest thickness.
When Louis Agassiz proposed his Glacial Theory in 1837 most people were skeptical that in the past large masses of ice had covered low plains in northern Europe. Agassiz’s evidence was what the glaciers left behind after melting: large boulders scattered across the countryside. 365betÌåÓýÔÚÏßÊÀ½ç±, geologists call such boulders erratics, which are rocks that do not match local bedrock and are too large to have been transported by rivers or ocean currents.
Richard Holm mapped the geology of the San Francisco Peaks, while teaching geology at Northern Arizona University. Post-retirement, Richard was a Roving Ranger for a couple of seasons and did additional geologic mapping in coordination with the Arizona Geologic Survey.
The NPS/USFS Roving Rangers volunteer through a unique agreement between the Flagstaff Area National Monuments and the Coconino National Forest to provide Interpretive Ranger walks and talks in the Flagstaff area each summer.
Submit questions for the ‘Ask a Ranger’ weekly column to [email protected].
“If rates were approved here and we started to see a negative impact on parking because people thought they were too high, it’s very easy for us to go back to the council and say, ‘Hey, we’d like to drop these back down to where they were compared to what it is to raise them." -- airport director Brian Gall Read moreAirport Commission approves increased parking rates, proposal sent to Flagstaff City Council
