This coverage dataset represents the existing Bureau of Land Management (BLM) Areas of Critical Environmental Concern (ACEC) in California. Areas of critical environmental concern are designated by the BLM under the requirements of the Federal Land Policy and Management Act (FLPMA). This designation depicts areas where special management attention is required to prevent significant damage to important ecological and cultural resources, or due to natural hazards that require special management. Special management practices are defined for these areas through the BLM's land management planning process. Areas of critical environmental concern are nominated by individuals or organizations within or outside the BLM. These areas are then ranked according to relevance and importance criteria by an interdisciplinary team within the BLM, and considered in an array of Resource Management Plan alternatives, within which the need for special management and its effects are assessed within the environmental analysis. Research natural areas are designated to preserve examples of significant natural ecosystems, to provide areas for environmental education and research, and to preserve significant gene pools of plant and animal species. Research areas are typically allowed to be dominated by natural processes with minimal human intervention.