The purpose of this study was to estimate the extent of petrified wood theft at two popular petrified wood sites at Petrified Forest National Park and to describe the nature of the thieves in terms of their level of moral reasoning. A model of noncompliant behavior was developed that incorporated the theory of reasoned action, the theory of planned behavior, the theory of attitude accessibility, and the four-compartment model of morality. The model proved valuable in understanding petrified wood theft. Data were collected by non-obtrusive observations. brief on-site interviews, and an eleven-page mailback questionnaire. In total, 226 park visitors (125 thieves and 101 non-thieves) were observed. Of these, 145 (77 thieves and 68 non-thieves) agreed to be interviewed and were given a questionnaire. Altogether, 116 (61 thieves and 55 non-thieves) returned a completed questionnaire for a combined response rate of 80.9 percent. A total of 456 park visitors, who were not observed, were also contacted and given a mailback questionnaire. Of these, 365 returned a completed questionnaire for a 80.0 percent response rate. An average of 1.02 thefts were observed per hour of observation at the two petrified wood sites. And, 1.22 percent of visitors at the two petrified wood sites collected at least one piece of petrified wood. An average of 1.6 pieces of petrified wood were taken per theft. These findings emphasize the seriousness of petrified wood theft by park visitors. Thieves were found to be significantly more thoughtless than non-thieves as measured by an impulsiveness scale. Also, thieves scored significantly higher than non-thieves on the preconventional level of moral reasoning scale. The findings imply that intervention programs which access desired attitudes toward petrified wood and establish a credible threat of punishment will be the most effective in reducing petrified wood theft. / Master of Science