Digital Data From the Leadville/Buena Vista 

Aeromagnetic Survey Covering Parts of Chaffee, 

Eagle, Lake, Park, and Summit Counties, 

Colorado 

By Viki Bankey and Goldak Airborne Surveys 

Open-File Report 2006–1327 

U.S. Department of the Interior 

U.S. Geological Survey 
U.S. Department of the Interior 

DIRK KEMPTHORNE, Secretary 

U.S. Geological Survey 

Mark D. Myers, Director 

U.S. Geological Survey, Reston, Virginia 2006 

For product and ordering information: 

World Wide Web: http://www.usgs.gov/pubprod 

Telephone: 1-888-ASK-USGS 

For more information on the USGS—the Federal source for science about the Earth, 

its natural and living resources, natural hazards, and the environment: 

World Wide Web: http://www.usgs.gov 

Telephone: 1-888-ASK-USGS 

Suggested citation: 

Bankey, Viki, and Goldak Airborne Surveys, 2006, Digital data from the Leadville/Buena Vista aeromagnetic 

survey covering parts of Chaffee, Eagle, Lake, Park, and Summit Counties, Colorado: U.S. Geological Survey 

Open-File Report 2006-1327. 

Any use of trade, product, or firm names is for descriptive purposes only and does not imply 

endorsement by the U.S. Government. 

Although this report is in the public domain, permission must be secured from the individual 

copyright owners to reproduce any copyrighted material contained within this report.

ii
Digital Data From the Leadville/Buena Vista 

Aeromagnetic Survey Covering Parts of Chaffee, 

Eagle, Lake, Park, and Summit Counties, Colorado 

By Viki Bankey1

 and Goldak Airborne Surveys2

Abstract 

This report contains digital data, image files, and text files describing data formats and 

survey procedures for aeromagnetic data collected during an aeromagnetic survey in central 

Colorado in October and November, 2002. 

Introduction 

This report describes data collected from an aeromagnetic survey flown over an area of 

central Colorado that includes parts of Chaffee, Eagle, Lake, Park, and Summit Counties, including 

the towns of Leadville and Buena Vista and parts of the Mosquito Range, Gore Range, and 

Sawatch Mtns. These data were collected by Goldak Airborne Surveys on contract to the U.S. 

Geological Survey (USGS). 

These surveys were designed to complete or extend the coverage of surveys previously 

acquired in Colorado (Oshetski and Kucks, 2000). Our overall objective in conducting these 

surveys is to improve knowledge of the subsurface geologic framework in an area of complex and 

intersecting structural terranes. In this area, the north-trending structures of the Rio Grande rift 

intersect the older, northeast-trending Colorado Mineral Belt. 

Organization of Data 

The "readme.txt" file provides summaries of the file contents. The folders are organized as 

follows. Files pertaining to this report are contained in the "report" folder; files pertaining to the 

gridded data are contained in the "grids" folder; files pertaining to the flight-line data are contained 

in the "linedata" folder; and files pertaining to the color shaded relief images are contained in the 

"images" folder. In the data folders, ASCII files with the extension “.txt” describe the format and 

contents of the data files. Please read the ".txt" files before using the data files.

 

1

 U.S. Geological Survey, Denver, CO. 

2

Contractor, Saskatoon, Saskatchewan, Canada. 

1
Description of Data 

Aeromagnetic data are collected using airborne geophysical sensors that measure subtle 

variations in the Earth’s magnetic field. Aeromagnetic surveys are designed to map the variations 

caused by the irregular distribution of naturally occurring magnetic minerals associated with 

geologic features. 

The aeromagnetic survey (fig. 1) employed a fixed-wing aircraft flying along traverse lines 

oriented east-west, spaced 400 m (about 1,300 ft) apart, and flown at a nominal 400 m (1,300 ft) 

above ground. Orthogonal tie lines were flown north-south at a 3,200 m (10,500 ft) spacing. Total 

flight-line coverage was 11,448 km (7,113 mi). The east-west orientation of traverse lines was 

chosen because it is oblique to the predominant northerly geologic strike of the area. The flight-line 

data from the contractor are included in this report. Contractor-provided details of the flight 

specifications, survey procedures, and data processing are included in Appendix A. 

A simplified digital elevation grid is provided to represent the ground surface. 

Data Processing 

Initial data processing and data reduction were accomplished by the contractor (Appendix 

A). The additional data and grid processing described in this section was done to display maximum 

detail while removing unwanted noise and simulating a flying surface draped at a consistent level 

over terrain. 

The magnetic data were interpolated onto a grid at 100 m intervals. Map projection is 

Universal Transverse Mercator (UTM), zone 13 (central meridian of 105o W longitude, a false 

easting of 500,000 m, a false northing of 0 m), and North American Datum of 1927 (NAD27). 

A standard reduction-to-pole operator was applied to the grid. This operation, resulting in 

reduced-to-pole (RTP) data, corrects for shifts of the main anomaly from the center of the magnetic 

source that occur at most latitudes owing to the oblique orientation of the measured magnetic field 

with respect to the Earth’s surface (the field is vertical only at the magnetic poles). Declination and 

inclination of the Earth's field were assumed to be 10.5o

 and 66 o respectively for this area. To 

apply the reduced-to-pole transformation, one must assume that the total magnetizations of most 

rocks in the study area align parallel or anti-parallel to the Earth's main field. 

References Cited 

Oshetski, K.C., and Kucks, R.P., 2000, Colorado aeromagnetic and gravity maps and data—A web 

site for distribution of data: U.S. Geological Survey Open-File Report 00-0042. [available online 

at: http://pubs.usgs.gov/of/2000/ofr-00-0042/colorado.htm]. 

2