Soil chemistry and depth are also important factors that influence where plants grow. Deep soils tend to be covered with grasses. Shrubs like blackbrush and purple sage favor shallow sandy soil, while greasewood and Mormon tea are signs of alkalinity. The dominant plant community in Arches, the pinyon-juniper woodland, colonizes rocky soils and fractured bedrock. Non-native plant species can also be found at Arches. Tamarisk lines waterways throughout the Colorado River drainage system with its feathery foliage, and Russian thistle (also known as tumbleweed) lines many trails and roadsides with its distinctive thorns.