Read Zion National Park:

In 1917, Horace Albright visited the canyon created by the Virgin River in southwestern Utah. He was amazed at the beauty of the colorful cliffs. Albright determined that this national monument would become a popular tourist destination. The official name of the monument at that time was Mukuntuweap National Monument. It had been named in honor of the Paiutes who lived in the region. Albright thought that the name was difficult to pronounce and proposed a name change. President Woodrow Wilson renamed the monument Zion National Monument, which became Zion National Park in 1919. The number of people visiting the park increased from approximately 300 in 1914 to 1,814 people in 1919.

Zion National Park is known for its many hiking trails. The shortest trail leads to one of the popular destinations: Weeping Rock, a cliff face with a hanging garden. Over the years, water made its way through the Navajo sandstone of the cliff, traveling through pores and creating canyons. Eventually, the water encountered a layer of rock that was impermeable. The water was unable to continue down, so it traveled horizontally. At Weeping Rock, the water comes through the pores of the sandstone. The amount of water that flows out of the rock can be a trickle or a stream, giving the impression that the rock is crying. Vegetation grows in shaded areas of the cliff with water coming through the rock. As the plants grow out of the rock face, they give the illusion that they are hanging in the air.

In the last century, word spread of Zion National Park's many natural treasures, like the Weeping Rock. Roads, trails, and visitor centers were built. More people traveled to Zion in order to hike, horseback ride, and go canyoneering. The Zion-Mount Carmel Tunnel was constructed by 1930. Visitors still use the tunnel to travel from Zion to the Grand Canyon or Bryce Canyon. Now, park rangers are facing problems created by having too many visitors. Trails and campgrounds are overused and need repairs. Visitors are straying off the trails to create their own, thereby damaging the vegetation. Rangers are considering the best ways to protect this national park and maintain its beauty for future generations.

Select the sentence from the text that explains the cause of Weeping Rock's unusual water flow.