The region is notable for its karst topography and tall rugged hills of limestone or granite. Many of the hills rise to a height of above the surrounding plains and valleys, with Packsaddle Mountain rising to a height of above the Llano River in Kingsland. The Hill Country also includes the Llano Uplift and the second-largest granite dome in the United States, Enchanted Rock. The terrain throughout the region is punctuated by a thin layer of topsoil and many exposed rocks and boulders, making the region very dry and prone to flash flooding. Native vegetation in the region includes various yucca, prickly pear cactus, desert spoon, and wildflowers in the Llano Uplift. The predominant trees in the region are ashe juniper and Texas live oak.