Grasses are one of the most important plants within the grassland ecosystem found in the park. Large expanses of grasslands form where wind-blown sediment and erosion have created a layer of soil several feet thick. One of the most devastating causes of grassland destruction is grazing by cattle and horses. Because grazing is not allowed within the park, the area has returned to a more natural state and is one of the largest recovering grasslands in the Southwest.

Individual grasses sprout almost anywhere they can find soil, even in potholes filled with dirt. Most grasses fit into two basic groups, bunch grass and sod-forming grass. Bunch grass is classic arid adapted grass occurring in scattered clumps. Its spreading growth pattern reduces competition for limited soil nutrients and water. Examples of bunch grass include rice grass and needle-and-thread grass. The large rice grass seeds are rich in protein and were an important source of food for American Indians. Needle-and-thread grass has a sharp seed attached to a thin thread-like tail which develops in a spiral, wound fashion. As the thread unwinds, it drives the seed into the ground. Both of these grasses are perennial, becoming dormant during droughts. Rice grass plants have been known to live over 100 years, through wet and dry times.

Sod-forming grass is what most people have in their yards. Galleta and Blue Grama, sod-forming perennials native to Petrified Forest National Park, usually grow together. Cheat grass was accidentally brought to the United States in the 1800s and is now found throughout the park.

To visitors unaccustomed to the vast landscapes of the Southwest, Petrified Forest National Park can seem somewhat barren. On closer look, the land is teeming with interesting and clever life.