After the surprise, Shelton takes Oprah and Gayle to one of Yosemite's most awe-inpsiring viewpoints, Tunnel View. 

When Oprah, Gayle, Shelton and the crew arrive, they are shocked to find three tour buses of visitors. "There are people coming out of the woodwork and I'm not even thinking about the show or the shots," Lisa says. "I just want to make sure [Oprah's] fine and OK."

Watch Lisa's team try to control the crowd 

Meanwhile in Chicago, Jon Stewart has gone missing and it's up to producer Jack's team to find him. Start the search for Jon Stewart