Pinyon-juniper woodland is the most common forest type in the American Southwest, covering over 40 million hectares (100 million acres) in ten states, and extending south into Mexico, and north into Idaho, Oregon, and Wyoming. Defined by the presence of one or more species of pinyon pine (Pinus spp.) and juniper (Juniperus spp.), this forest type is associated with a range of different vegetation. The majority of pinyon-juniper woodlands are found in regions subject to temperature extremes and limited moisture availability.