The Lassen interstate mule deer (Odocoileus hemionus) herd ranges from the northwestern area of Nevada to the northeastern corner of California along the western rim of the Great Basin. This mule deer herd serves as a model for what has happened in terms of population dynamics for many Intermountain west mule deer populations. Before contact with Europeans the populations were apparently very restricted. After the introduction of domestic livestock there has been significant impacts on the relative abundance of shrubs versus perennial grasses. Mule deer herds underwent tremendous expansion which peaked in the 1950s. Recent mule deer population numbers in the Lassen interstate herd have sharply declined. These population dynamics can be related to several habitat changes that reflect increased frequencies of wildfires in lower elevational sites as shrubs became old and decadent. Lack of fire in the higher elevations resulted in decadent/senscent old shrub stands. Invasion by exotic annual grasses in lower elevational sites. In certain environments, sharply improved range condition due to grazing management systems. The increase in coniferous woodlands, which may reflect changes in climate and/or atmospheric gases, combined with the lack of fire significantly negatively impact the Lassen Interstate mule deer herd. Identifying the specific aspect of winter, transitional, and/or summer habitat, in terms of dietary deficiency, that are most closely related to the decline in mule deer numbers is a highly significant problem facing wildlife and range managers.