The rooting habit of pinyon is characterized by both lateral and vertical root systems (67), but roots of pinyons less than 3 m (10 ft) tall have been traced to depths 6.4 m (21 ft) in underlying rock (25). Taproots and some laterals that penetrate downward, however, grow horizontally when they encounter an impenetrable horizon or bedrock. Laterals develop at a depth of about 15 to 41 cm (6 to 16 in) and can exceed the crown radius by a factor of two or more. Taproot growth of seedlings is rapid, averaging 17 to 27 cm (7 to 11 in) in length for 1-year-old seedlings (35). The extensive root system and relatively rapid rate of root elongation, especially of young seedlings, enhance the ability of pinyon to survive under and environments.
Burns, Russell M., and Barbara H. Honkala, technical coordinators. 1990. Silvics of North America: 1. Conifers; 2. Hardwoods. Agriculture Handbook 654 (Supersedes Agriculture Handbook 271,Silvics of Forest Trees of the United States, 1965). U.S. Department of Agriculture, Forest Service, Washington, DC. vol.2, 877 pp.