In conjunction with integrated mapping of the Oligocene central San Juan caldera cluster, southwestern Colorado (USGS I-Map 2799, in press), all modern chemical analyses of volcanic rocks for this area determined in laboratories of the U.S. Geological Survey have been re-evaluated in terms of the stratigraphic sequence as presently understood. These include approximately 700 unpublished analyses made between 1986 and 2003, as well as all USGS analyses published since 1965 when the widespread presence of regional welded ash-flow tuffs erupted from large calderas was first recognized. All the analyses are assigned unit identifiers consistent with those used for the new geologic map; quite a few of these differ from those used on sample submittal forms and in prior USGS publications.
Download the text portion of this report as a PDF document (212 KB)
Download the table to accompany this report as Microsoft Excel .xls document (1 MB)
For questions about the content of this report, contact Peter Lipman
| PDF help
| Publications main page | Open-File
Reports for 2004 |