[1] Geochemical variation in the less than 5 Ma Wrangell Volcanic Field, Alaska, with an emphasis on the Skookum Creek volcanic complex, 1997

Preece, S. J., 1997, Geochemical variation in the less than 5 Ma Wrangell Volcanic Field, Alaska, with an emphasis on the Skookum Creek volcanic complex: Miami University (Ohio) unpublished Ph.D. dissertation, 547 p.

[2] Changing ideas on the identity and stratigraphic significance of the Sheep Creek tephra beds in Alaska and the Yukon Territory, northwestern North America, 2008

Westgate, J.A., Preece, S.J., Froese, D.G., Pearce, N.J.G., Roberts, R.G., Demuro, M., Hart, W.K., and Perkins, W., 2008, Changing ideas on the identity and stratigraphic significance of the Sheep Creek tephra beds in Alaska and the Yukon Territory, northwestern North America: Quaternary International, v. 178, n. 1, p. 183-209, doi: 10.1016/j.quaint.2007.03.009.