The Chihuahuan Desert covers about 80% of the park and surrounds the Chisos Mountains. Bare, rocky ground and sparse vegetation are hallmarks of the desert, but there is plenty of life here. Look for termite nests along plant stems, exoskeletons of millipedes, animal scat, and rodent and reptile tunnels. Bird life is plentiful, especially in the morning; look for nests hidden in yuccas and cacti. In the spring, bluebonnets, paintbrush, bi-color mustard, desert marigold, yucca, ocotillo, and cacti blossoms add color to the desert landscape.