Kbqm
Butte Quartz Monzonite (Late Cretaceous)
Kal
Alaskite and related felsic rocks (Late Cretaceous)
Qa
Alluvium (Holocene)
Qgt
Glacial till, undivided (Holocene and Pleistocene)
Kmo
Mafic igneous rocks, undivided (Late Cretaceous)
Kevm
Elkhorn Mountains Volcanics, middle member (Upper Cretaceous)
Kgd
Granodiorite (Late Cretaceous)
Keva
Elkhorn Mountains Volcanics, ashflow tuff, present in Kevm (Upper Cretaceous)
Ki
Andesitic intrusive rocks related to Elkhorn Mountains Volcanics (Late Cretaceous)
Qt
Terrace gravel (Holocene and Pleistocene)
Kevl
Elkhorn Mountains Volcanics, lower member (Upper Cretaceous)
Qc
Colluvium (Holocene)
QTg
Older gravel (Pleistocene or Pliocene)
Qoa
Old alluvium (Holocene and Pleistocene)
MIOGs
!@s
Sedimentary rocks, undivided (Miocene and Oligocene)
MIOGsc
!@sc
Sedimentary rocks, undivided (Miocene and Oligocene), covered with discontinuous veneer of gravel, sand, and loess
Water
Open water
QTp
Older pediment gravel, undivided (Pleistocene or Pliocene)
OGr
@r
Rhyolite, shallow intrusive bodies and flows (Oligocene)
Ygl
Greyson Formation, lower member (Mesoproterozoic)
Yn
Newland Formation, undivided (Mesoproterozoic)
Qp
Pediment gravel (Pleistocene)
QTa
Older alluvium (Pleistocene and Pliocene(?))
Kqm
Quartz monzonite (Late Cretaceous)
Ynl
Newland Formation, lower part (Mesoproterozoic)
MIOGf
!@f
Fort Logan Formation (Miocene and Oligocene)
Ygm
Greyson Formation, middle member (Mesoproterozoic)
Yg
Greyson Formation, undivided (Mesoproterozoic)
dt
Dredge or placer tailings
Ynu
Newland Formation, limestone-bearing upper part (Mesoproterozoic)
Qac
Alluvium and colluvium, undivided (Holocene)
Kqd
Quartz diorite (Late Cretaceous)
Km
Monzonite (Late Cretaceous)
Kevu
Elkhorn Mountains Volcanics, upper member (Upper Cretaceous)
Tl
Lamprophyre (Tertiary(?))
Kg
Granite (Late Cretaceous)
Qbg
Boulder gravel (Holocene and Pleistocene)
Ql
Landslide deposit (Holocene and Pleistocene)
Ks
Slim Sam Formation (Upper Cretaceous)
EOql
#ql
Quartz latite (Eocene)
Qgty
Glacial till, younger till where more than one age of till is recognized (Pleistocene)
Kc
Colorado Group, sedimentary rocks, undivided (Upper and Lower Cretaceous)
af
Artificial fill
Qog
Old gravel (Holocene and Pleistocene)
QTp2
Older pediment gravel, upper level overlying rocks of Miocene or older age (Pleistocene and Pliocene)
Kbqmf
Alaskite and related felsic rocks with Butte Quartz Monzonite (Late Cretaceous)
QTp1
Older pediment gravel, lower level where two levels of gravel are adjacent (Pleistocene or Pliocene)
OGb
@b
Basalt (Oligocene)
Ygu
Greyson Formation, upper member (Mesoproterozoic)
Kcu
Colorado Group, upper part (Upper and Lower Cretaceous)
Kbqmm
Butte Quartz Monzonite, medium grained (Late Cretaceous)
Qag
Alluvium and glacial till, undivided (Holocene and Pleistocene)
Kl
Lamprophyre (Late Cretaceous)
Kad
Andesite and diorite intrusive rocks (Late Cretaceous)
Kcm
Colorado Group, middle part (Lower Cretaceous)
Kev
Elkhorn Mountains Volcanics, undivided (Upper Cretaceous)
Ys
Spokane Formation (Mesoproterozoic)
Qgtc
Older glacial till and associated colluvium (Pleistocene)
Kcl
Colorado Group, lower member (Lower Cretaceous)
Kk
Kootenai Formation (Lower Cretaceous)
Jme
Morrison Formation and Ellis Group, undivided (Jurassic)
Ksd
Syenodiorite (Late Cretaceous)
Kd
Diorite porphyry (Late Cretaceous)
PMab
*Mab
Amsden Formation  (Pennsylvanian) and Big Snowy Group (Upper Mississippian), undivided
Pq
*q
Quadrant Formation (Pennsylvanian)
Pp
Phosphoria Group (Permian)
Pa
*a
Amsden Formation  (Pennsylvanian)
Je
Ellis Group, undivided (Jurassic)
Mm
Mission Canyon Limestone (Upper and Lower Mississippian)
Qgto
Glacial till, older till where more than one age of till is recognized (Pleistocene)
PPpq
P*pq
Phosphoria Group (Permian) and Quadrant Formation (Pennsylvanian), undivided
Cpi
_pi
Pilgrim Formation (Upper Cambrian)
DCm
D_m
Maywood Formation (Upper and Middle Devonian), locally includes some Cambrian rocks
Dj
Jefferson Formation (Upper Devonian)
Ml
Lodgepole Limestone (Lower Mississippian)
Cp
_p
Park Formation (Upper and Middle Cambrian)
Cm
_m
Meagher Limestone (Middle Cambrian)
Cw
_w
Wolsey Formation (Middle Cambrian)
Cf
_f
Flathead Sandstone (Middle Cambrian)
Ye
Empire Formation (Mesoproterozoic)
MDt
Three Forks Formation (Lower Mississippian and Upper Devonian)
Zd
Diorite (Neoproterozoic)
Kb
Basalt (Late Cretaceous)
MIOGts
!@ts
Vitric tuff and tuffaceous sedimentary rock (Miocene and Oligocene)
Qpw
Pediment gravel with veneer of windblown sand and silt (Pleistocene)
Cpp
_pp
Pilgrim Formation (Upper Cambrian) and Park Shale (Upper and Middle Cambrian), undivided
POMIs
~!s
Sedimentary rocks, undivided (Pliocene and Miocene)
Du
Upper and Middle Devonian rocks, undivided
MIOGs1
!@s1
Sedimentary rocks, orange-red conglomerate and sandstone tongue (Miocene and Oligocene)
OGs2
@s2
Climbing Arrow Formation, upper part (Oligocene)
OGs1
@s1
Climbing Arrow Formation, lower part (Oligocene)
OGs3
@s3
Dunbar Creek Formation (Oligocene)
Mmu
Madison Group, undivided (Upper and Lower Mississippian)
Jm
Morrison Formation (Jurassic)
Ktc
Telegraph Creek Formation (Upper Cretaceous)
Ke
Eagle Sandstone (upper Cretaceous)
Kma
Maudlow Formation, unit a (Upper Cretaceous)
Kmb
Maudlow Formation, unit b (Upper Cretaceous)
Kmc
Maudlow Formation, unit c (Upper Cretaceous)
Kmd
Maudlow Formation, unit d (Upper Cretaceous)
Kme
Maudlow Formation, unit e (Upper Cretaceous)
Kmf
Maudlow Formation, unit f (Upper Cretaceous)
Mb
Big Snowy Group, undivided (Upper Mississippian)
Kmg
Maudlow Formation, unit g (Upper Cretaceous)
QTb
Basalt (Pleistocene(?) or Pliocene(?))
Kwqm
Quartz monzonite of the Wilson Peak pluton (Late Cretaceous)
Kmh
Maudlow Formation, unit h (Upper Cretaceous)
MIOGs2
~!s2
Sedimentary rocks, sandstone and conglomerate tongue (Miocene and Oligocene)
Yl
Lahood Formation (Mesoproterozoic)
Cwf
_wf
Wolsey Formation and Flathead Sandstone, undivided (Middle Cambrian)