Castle Rock is a 4,321-foot (1,317 meter) elevation sandstone summit located in Glen Canyon National Recreation Area, in Kane County of southern Utah. It is situated 6.5 miles (10.5 km) north of the town of Page, and 2.5 miles (4.0 km) northeast of the Wahweap marina. Castle Rock towers over 600 feet above Lake Powell, and becomes an island when the lake is full. This iconic landmark of the Lake Powell area is composed primarily of Entrada Sandstone. This sandstone, which was originally deposited as sandy mud on a tidal flat, is believed to have formed about 160 million years ago during the Jurassic period as a giant sand sea, the largest in Earth's history.