Dean Karnazes, 48, expects to average 50 miles of running per day, saying this was his most intense endeavor yet.
His efforts are for Action for Healthy Kids.
"It's to motivate and inspire kids to get more active, to get them physically moving," Kamazes said.
People can sign up to run with Kamazes by going to http://www.dadt.com/live/special/runacrossamerica/index.html. He will be running in Riverside on Saturday.
Karnazes' coast-to-coast run is scheduled to end on May 11 in New York City.