Northern Guam geospatial information server
About this map:
This is a detailed geologic map of northern Guam, showing all the recognized stratigraphic units: formations, members, and facies. The map is based on the newest geologic map of Guam by Siegrist, H.G. and Reagan, M. (2008), who updated and revised the original Geologic Map of Guam by Tracey et al. (1964). Reinterpretation and revision of the map utilized a wealth of new data, including radiometric dating of selected volcanic rocks and a thin-section study of new limestone specimens. The work resulted in a single 1:50,000-scale map, as well as nine 1:24,000 scale maps, corresponding to the USGS 7.5-minute quadrangles that cover the island of Guam. The maps were published in early 2008 and were scanned, georeferenced, and digitized to produce GIS shapefiles.