Adams, R.P., S. Nguyen, J.A. Morris and A.E. Schwarzbach. 2006. Re-examination of the taxonomy of the one-seeded, serrate leaf Juniperus of southwestern United States and northern Mexico (Cupressaceae). Phytologia 88(3):299-310.
Nearly all of R.P. Adams' publications are available online as PDF files. Go to http://www.juniperus.org/articles.html, and search for the paper in question.