About 2,500 people are expected to take off early Saturday on a 200-mile bicycle race through the Flint Hills.

The Wichita Eagle reports the Dirty Kanza race started 12 years ago go with 36 riders but it has grown into an endurance race that brings in an estimated $2.2 million every spring.

The race starts and ends in Emporia. It is named after the crunchy Flint Hills gravel on the route, which makes racers filthy. This year’s participants include world champion endurance racer Rebecca Rusch and competitors from 10 countries and 46 states.

Riders climb as much as 1,200 feet on the route, often into the constant Kansas winds.

Organizer Casey Wood says the race is so difficult only about half the starters finish, even fewer if it rains.