The Kentucky River flows almost 225 miles from its origin near Pine Mountain in eastern Kentucky to Carrollton, where it joins the Ohio. In the Bluegrass, between Frankfort and Boonesborough, the meandering river is framed by palisades, imposing cliffs that rise more than 250 feet above the river's surface. Formed over several million years as the river cut slowly downward into hard limestone and dolomite, these rocks are about 460 million years old and are the oldest exposed surface rocks in Kentucky. The wooded corridors of the Kentucky River Palisades ecosystem serve as a migration route for birds and a travel corridor for wildlife, and they are home to several endangered plants, including cleft phlox and mountain lover. Salamanders found nowhere else in central Kentucky live high above the river, and four species of endangered bats, including gray bats, Indiana bats, and the rare Keen's bat, inhabit the cliff caves. The only natural vegetation remaining in the Inner Bluegrass Region is found in this ecosystem. The Kentucky River also inspired artists, most notably Paul Sawyier, who was born in 1865, grew up in Frankfort, studied art in Cincinnati and New York, returned to Kentucky in 1891, and concentrated on landscape painting, primarily in watercolor. Between 1908 and 1913 he spent much of his time on the Kentucky River, living and working aboard a houseboat docked at the foot of High Bridge, where he created some of his most popular paintings.