Climate is considered the primary control on plant life, but within a particular climatic region the rock beneath soil—known as the parent material of soil—is typically the key factor influencing the vegetation growing above. Rock ultimately determines soil moisture characteristics, nutrient availability, and concentrations of essential elements.
Therefore, certain plants are associated with specific rock types. Limestone, dolomite, shale, gypsum, chert, gabbro, rock salt, and ultramafic rocks (e.g., dunite, peridotite, serpentinite), for example, are known for their distinctive floras. Since before the advent of agriculture humans have used plants as a guide to find sought-after rocks and minerals. Today, the methodologies of geobotany are still applicable, practical, and even cost-effective to the geologist.
Dramatic changes in vegetation can occur with changes in geology. In mountain ranges of the Great Basin, big sagebrush growing on sandstone abruptly transitions to bristlecone pine on dolomite. The distribution of the California poppy in Arizona closely correlates with copper mineralization, which in turn corresponds with fault lines.