Posted by ESPN.com's Bill Williamson
The stout Johnson, from Colorado State, was drafted by San Diego in the fourth round. He will give the Chargers a power running presence.
Malcolm Floyd was not at the mandatory camp. He is a restricted free agent who has not signed his tender. Because Floyd, a reserve receiver, doesn't have much choice, expect him to eventually sign and report.
There is no update on a potential contract extension for Rivers. He is signed through this season.
Defensive end Vaughn Martin was closely watched by the media Friday. He looked fast and he is clearly big and strong. He was a surprise fourth-round choice of Western Ontario. He is raw, but he is an interesting project.