US Migrating
type: Agent

Transient electromagnetic (TEM) sounding data; San Luis Valley, Colorado, 2007
type: Dataset
contact point: Organization
  fn: V.J. (Tien) Grauch
keyword: geophysics
keyword: subsurface-maps
keyword: clay-deposits
keyword: united-states
keyword: faulting-geologic
keyword: geo
keyword: usgs-5841bc82e4b04fc80e518c62
keyword: electromagnetic-surveying
keyword: clay
keyword: national
keyword: transient-electromagnetic-sounding
keyword: geoscientificinformation
keyword: subsurface-mapping
keyword: north-america
keyword: great-sand-dunes-national-preserve
keyword: geoss
keyword: amerigeoss
keyword: san-luis-valley
keyword: saguache-county
keyword: alamosa-national-wildlife-refuge
keyword: amerigeo
keyword: groundwater
keyword: fault-detection
keyword: ckan
keyword: great-sand-dunes-national-park
keyword: alamosa-county
keyword: tem
keyword: aquifer
keyword: colorado
theme: {geospatial}
description: Transient electromagnetic (TEM) soundings were made in the San Luis Valley, Colorado, to map the location of a blue clay unit as well as to investigate the presence of suspected faults. A total of 147 soundings were made near and in Great Sand Dunes National Park and Preserve, and an additional 6 soundings were made near Hansen Bluff on the eastern edge of the Alamosa National Wildlife Refuge. The blue clay is a significant hydrologic feature in the area that separates an unconfined surface aquifer from a deeper confined aquifer. Knowledge of its location is important to regional hydrological models. Previous analysis of well logs has shown that the blue clay has a resistivity of 10 ohm-meters or less, which is in contrast to the higher resistivity of sand, gravel, and other clay units found in the area, making it a very good target for TEM soundings. The top of the blue clay was found to have considerable relief suggesting the possibility of deformation of the clay during or after deposition. Because of rift activity deformation is to be expected. Of the TEM profiles made across faults identified by aeromagnetic data, some showed resistivity variations and (or) subsurface elevation relief of resistivity units suggestive of faulting. Such patterns were not associated with all suspected faults. The Hansen Bluff profile showed variations in resistivity and depth to conductor that coincide with a scarp between the highlands to the east and the floodplain of the Rio Grande River to the west.
issued: 2025-11-22T09:25:18.376191
modified: 20200929
spatial: Location

Digital Data
type: Distribution
access URL: https://dx.doi.org/10.5066/F7D21VQ5
media type: application/http
description: Landing page for access to the data
format: XML
issued: 2022-08-07T08:16:29.439068
modified: 2025-11-22T09:25:18.357174

Original Metadata
type: Distribution
access URL: https://data.usgs.gov/datacatalog/metadata/USGS.5841bc82e4b04fc80e518c62.xml
media type: text/xml
description: The metadata original format
format: XML
issued: 2022-08-07T08:16:29.439062
modified: 2025-11-22T09:25:18.356664