Data release for the geologic map of the upper Arkansas
River valley region, north-central Colorado
Description
This 1:50,000-scale geologic map represents a compilation
of the most recent geologic studies of the upper Arkansas
River valley, between Leadville and Salida, Colorado. The
valley is structurally controlled by an extensional fault
system that forms part of the prominent northern Rio Grande
rift, an intra-continental region of crustal extension. This
work also incorporates new detailed geologic mapping of
poorly understood areas within the map area and reinterprets
previously studied areas, aided by lidar data that covers 59
percent of the map area. The mapped region extends into the
Proterozoic metamorphic and intrusive rocks in the Sawatch
Range west of the valley and the Mosquito Range to the east.
Paleozoic rocks are preserved along the crest of the Mosquito
Range, but most of them have been eroded from the Sawatch Range.
Numerous new isotopic ages (U-Pb zircon ages for the intrusive
Proterozoic and some Tertiary rocks adjacent to the valley and
40Ar/39Ar ages for the Late Cretaceous to Oligocene intrusive
and extrusive rocks) better constrain the timing of both
Proterozoic and Late Cretaceous to early Tertiary intrusive
events. The U-Pb ages document widespread ~1,440-Ma granitic
plutonism north of Buena Vista that produced batholiths that
intruded an older suite of ~1,760-Ma metamorphic rocks
and ~1,700-Ma plutonic rocks. As a result of extension
during the Neogene and possibly latest Paleogene, the graben
underlying the valley is filled with thick basin-fill deposits
(Dry Union Formation and older sediments), which occupy two
sub-basins, separated by a bedrock high near the small town
of Granite. The Dry Union Formation has undergone deep
erosion since the late Miocene or early Pliocene. During the
Pleistocene, ongoing steam incision by the Arkansas River and
its major tributaries has been interrupted by periodic
aggradation. From Leadville south to Salida as many as 7
mapped alluvial depositional units, which range in age from
early to late Pleistocene, record periodic aggradational events
along these streams that are commonly associated with
deposition of glacial outwash or bouldery glacial-flood
deposits. Many previously unrecognized Neogene and Quaternary
faults, some of the latter with possible Holocene displacement,
have been identified on lidar imagery. This imagery has also
permitted more accurate remapping of glacial, fluvial, and
mass-movement deposits and has aided in the determination of
their relative ages. Recently published 10Be cosmogenic
surface-exposure ages, coupled with new geologic mapping, have
revealed the timing and rates of late Pleistocene deglaciation.
Glacial dams that impounded the Arkansas River at Clear Creek
and possibly at Pine Creek failed at least 3 times during the
middle and late Pleistocene, resulting in catastrophic floods
and deposition of enormous boulders and bouldery alluvium
downstream; at least two failures occurred during the late
Pleistocene during the Pinedale glaciation.
Resources
| Name |
Format |
Description |
Link |
|
55 |
Landing page for access to the data |
https://doi.org/10.5066/F75B00XQ |
|
55 |
The metadata original format |
https://data.usgs.gov/datacatalog/metadata/USGS.5910ab8fe4b0e541a03ac85f.xml |