|
Two cute little peaks south of Fillmore. And such original names: looking west at South Twin Peak and North Twin Peak.
About 200 million years ago the area of present-day Millard County lay near sea level and was awash in shallow marine waters on a continental shelf upon which a stack of fossil-bearing strata more than 6 miles thick slowly accumulated.
Rhyolites from North Twin Peak show enough variation in composition to cause Crecraft and others (1981) to
uggest that it may consist of two discrete eruptions. In general the rock is 70 percent groundmass of quartz, feldspar, oxides, apatite, sphene, and zircon.
The South Peak (obviously the taller of the two): The groundmass consists of quartz, sanidine, plagioclase, oxides, and zircon. Hematite in the groundmass gives the rock its characteristic red color.
As I said previously: It is astonishing that there is this 324 page report on the Geology of Millard County. The 2003 bulletin is the product of over a half century of personal geologic studies in Millard County and contributions from numerous other researchers. : https://ugspub.nr.utah.gov/publications ... /B-133.pdf (rather technical, extremely thorough I'd say).
About 200 million years ago the area of present-day Millard County lay near sea level and was awash in shallow marine waters on a continental shelf upon which a stack of fossil-bearing strata more than 6 miles thick slowly accumulated.
Rhyolites from North Twin Peak show enough variation in composition to cause Crecraft and others (1981) to
uggest that it may consist of two discrete eruptions. In general the rock is 70 percent groundmass of quartz, feldspar, oxides, apatite, sphene, and zircon.
The South Peak (obviously the taller of the two): The groundmass consists of quartz, sanidine, plagioclase, oxides, and zircon. Hematite in the groundmass gives the rock its characteristic red color.
As I said previously: It is astonishing that there is this 324 page report on the Geology of Millard County. The 2003 bulletin is the product of over a half century of personal geologic studies in Millard County and contributions from numerous other researchers. : https://ugspub.nr.utah.gov/publications ... /B-133.pdf (rather technical, extremely thorough I'd say).