About this map:

This map shows geology of southern Guam in detail. Different colors and shadings stand for different geologic formations (types of rocks) exposed at the land surface. The map was created by U.S. Geological Survey (Tracey et al., 1964, Geology of Guam). The geologic abbreviations shown in the legend are standard used on Guam and stand for the following rock units:

Recent deposits:
Qaf - Artificial fill
Qal - Alluvium
Qrb - Beach deposits
Qrm - Merizo Limestone

Pliocene/Pleistocene limestone:
Qtma - Mariana Limestone Agana Argillaceous Member
Qtmd - Mariana Limestone Detrital Facies
Qtmf - Mariana Limestone Foraminiferal Facies
Qtmm - Mariana Limestone Molluskan Facies
Qtmr - Mariana Limestone Reef Facies

Miocene/Pliocene limestone:
Tal - Alifan Limestone
Tam - Mahlac Member
Tb - Bonya Limestone
Tbl - Barrigada Limestone
Tj - Janum Limestone
Tt - Talisay Member

Miocene volcanics:
Tub - Umatac Formation Bolanos Pyroclastic Member
Tud - Umatac Formation Dandan Flow Member
Tuf - Umatac Formation Facpi Volcanic Member
Tum - Umatac Formation Maemong Limestone Member

Eocene/Oligocene volcanics:
Ta - Alutom Formation