Diorite and gabbro (MTKdg;0)

State	Montana
Name	Diorite and gabbro
Geologic age	Phanerozoic \| Mesozoic \| Cretaceous(?)
Original map label	Kdg
Comments	Many unrelated intrusions are lumped into this map unit; most are probably Cretaceous in age, but some Tertiary rocks may be included.
Primary rock type	diorite
Secondary rock type	gabbroid
Other rock types
Lithologic constituents	Major Igneous > HypabyssalMany types of igneous forms are represented by this map unit, such as stocks, laccoliths, dikes, and sills. Likewise, a wide variety of igneous lithologies are included, not only mafic types. For example, the Lone Tree laccolith of Late Cretaceous age in the northern Madison Range consists mostly of dacite.
Map references	Ross, P.R., Andrews, D.A., and Witkind, I.J., 1955, Geologic map of Montana: U.S. Geological Survey, 2 sheets, scale 1:500,000.
Unit references	Lewis, R.S., 1998, Preliminary geologic map of the Butte 1° x 2° quadrangle: Montana Bureau of Mines and Geology Open File Report 363, 16 p, scale 1:250,000. Porter, K.W., Wilde, E.M., 1993, Preliminary geologic map of the Lewistown 30' x 60' quadrangle, revised 1999: Montana Bureau of Mines and Geology Open File Report 308, 22 p., scale 1:100,000. Wilson, A.B., and Elliott, J.E., 1997, Geologic maps of western and northern parts of Gallatin National Forest, south-central Montana: U.S. Geological Survey Geologic Investigations Series Map I-2584, 2 sheets, scale 1:126,720. [http://pubs.er.usgs.gov/publication/i2584] Mudge, M.R., Earhart, R.L., 1983, Geologic and structure maps of the Choteau 1° x 2° quadrangle, western Montana: United States Geological Survey Miscellaneous Geologic Investigations Series Map I-1300, scale 1:250,000. [http://pubs.er.usgs.gov/publication/i1300]
Geographic coverage	Broadwater - Flathead - Granite - Jefferson - Lewis and Clark - Madison - Powell - Teton