About this map:

This map shows the topographic divides that represent the boundaries of subsurface drainage basins of the Northern Guam Lens Aquifer (NGLA). Subsurface drainage is guided by topography of basement volcanic units that underlie the northern Guam limestone plateau. The source of the geospatial information is the 2013 volcanic basement map, an update of the original 1982 map produced by the Northern Guam Lens Study (CDM, 1982). The work on updating the map utilized geophysical and drilling data to correct and refine the understanding of basement topography and improve the map; see WERI Technical Report #141 (Bendixson, 2013). Details on the methodology used, content, and applications of the map can be found in WERI Technical Report #142 (Vann et al., 2013).