Geologically, Říp is the erosional remnant of a Late Oligocene volcano and is composed of basalt nephelites containing olivine granules, amphibole, leucite and — among others — magnetite, so a local magnetic anomaly can even be observed there by the compass. The hill was bare until 1879 when Mořic Lobkowitz had it planted with trees. Today, almost all of the mountain is covered by an oak-and-hornbeam forest with some maple, pine ash, and linden trees. Some rare thermophile plants can be found at the few tree-less places on the top of the hill, such as "Gagea bohemica" and "Iris pumila".