The Caribou-Poker Creeks Research Watershed is entirely underlain by the Yukon-Tanana metamorphic complex (formerly the Birch Creek Formation). This basement complex of meta-sedimentary rocks covers approximately 75 percent of the Yukon-Tanana Uplands. Chapman et al. (1971) described the complex in the watershed as a greenschist facies, dominated by chlorotic and quartz-mica schists, with some micaceous quartzites, garnet-mica schists, phyllites, and possible greenstone or impure marbles. Immediately south of the watershed in the Chatanika terrain (Metz 1981) of the Fairbanks mining district, the rocks consist of quartzite, quartz-mica schist, mica schist, marble, amphibolite, and calc-magnesium schist (Swainbank and Forbes 1975).
Mertie (1937) assigned the formation to the Precambrian era based on its unfossilized, highly recrystallized rocks and its relation to fossiliferous limestone deposits. However, more recent work by a number of investigators as cited by Hawkins et al. (1982) concluded that the sedimatary protoliths were deposited from late Precambrian through late Paleozoic. Areas east and south of the watershed are intruded by granitic batholiths of Cretaceous age while to the north and northeast unmetamorphosed Paleozoic sediments are found.
Radiometric dates in the Fairbanks mining district range from 102.5 plus or minus 3 million years to 478.5 plus or minus 35 million years (Forbes 1982), with differences explained by thermal resetting of the mica dates (Hall 1985). This, however, corresponds to the date of recrystallization and not the age of deposition.
Hall (1985) identified four distinct fold and fabric generating events in the Fairbanks mining district. The study compiled by Hall indicated a dominant northeast trend in the regional structure. Koutz and Slaughter (1972) reported similar findings in CPCRW. The research watershed underwent metamorphism during the emplacement of the Pedro Dome intrusion, which is composed of a phorphyritic granite that forms a northeast trending antiform.
Outcrops in the watershed are rare, usually confined to the upper slopes and ridges, with the largest near the summit of Haystack Mountain.
Glaciation occurred in central Alaska during the Illinoian and Wisconsin (Pewe 1965). The watershed was not glaciated, as the snowline for the two events were 1,220 meters and 1,370 meters respectively. With the snowline at such a high elevation for interior Alaska, only 3-5% of the Yukon-Tanana Uplands was glaciated (Pewe et al. 1967). The watershed was, however, affected by periglacial action as indicated by the presence of small solifluction lobes, subdued block fields, and tors (Koutz and Slaughter 1972).
Chapman, R.M, F.R. Weber, and B. Taber. 1971. Preliminary geologic map of Livengood quadrangle. U.S. Geological Survey. Open File Report 483. scale 1:250,000.
Forbes, R.B. 1982. Bedrock geology and petrology of the Fairbanks Mining District, Alaska. Alaska Division of Geological and Geophysical Surveys Open File Report 169. 69 pp.
Hall, M. 1985. Structural geology of the Fairbanks mining district. Master's thesis, University of Alaska. Fairbanks, Alaska. 68 pp.
Hawkins, D.B., R.B. Forbes, C.I. Hok, and D. Dinkel. 1982. Arsenic in the water, soil, bedrock, and plants of the Ester Dome area of Alaska. Institute of Water Resources. University of Alaska. Fairbanks, Alaska. Report IWR-103. 82 pp.
Koutz and Slaughter, 1972. Geological setting of the Caribou-Poker Creeks Research Watershed. Technical note. CRREL. 32 pp.
Mertie, J.B., Jr. 1937. The Yukon-Tanana region. U.S. Geological Survey. Bulletin 872. 276 pp.
Metz, P. 1981. Fluid inclusions and stable isotopic evidence for the origin of the Au-As-Sb-W mineralization of the Fairbanks mining district, Alaska. (Abstract). Geological Society of America. Abstracts with programs. Vol. 16 No. 1. p. 594.
Pewe, T.L. 1965. Fairbanks area. in Pewe, T.L., O.J. Ferrians, D.R. Nichols, and T.N. Karlstrom. INQUA Field Conference F, Central and South-Central Alaska. Guidebook: 6-36. Nebraska Academy of Science. Lincoln, Nebraska.
Pewe, T.L., L. Burbank, and L.R. Mayo. 1967. Multiple glaciation of the Yukon-Tanana Uplands, Alaska. U.S. Geological Survey. Misc. Investigations Map I-507. scale 1:500,000.
Ray, S.R. 1988. Physical and chemical characteristics of headwater streams at Caribou-Poker Creeks Research Watershed, Alaska. Master's thesis, University of Alaska. Fairbanks, Alaska. 172 pp.
Swainbank, R.D. and R.B. Forbes. 1975. Petrology of ecologitic rocks from the Fairbanks area, Alaska. Geological Society of America. Special Paper 151. pp 77-214.