It's a little more involved than that.
"From June 18 until June 24, 2009, the whereabouts of Governor Sanford were unknown to the public, including his wife and State Law Enforcement Division, which provides security for him. The absence of Governor Sanford was first reported by Jim Davenport of the Associated Press.[4][5] This six day disappearance garnered nationwide news coverage. His state and personal phones were turned off and he did not respond to phone or text messages. That prompted some to believe that he was missing and raised questions about who was acting as governor of South Carolina. His wife, Jenny Sanford, initially stated that she was not concerned and that he needed time away from their children to write something.[6] Sanford has apparently made similar disappearances in the past, although this was the longest.[7] After media speculation grew, Sanford's office on June 22 stated that he told them where he was going before he left and that he would be "difficult to reach."[8] Later that day, Sanford's spokesman, Joel Sawyer, told the press that Sanford was hiking the Appalachian Trail.[1]
Some South Carolina politicians voiced concerns about the governor's behavior. Lieutenant Governor André Bauer announced that he could not "take lightly that his staff has not had communication with him for more than four days, and that no one, including his own family, knows his whereabouts."[1] The Senate Minority Leader, Democrat John Land, also questioned the fact that Sanford was absent over the Father's Day weekend, arguing that "it's one thing for the boys to go off by themselves, but on Father's Day to leave your family behind? That's erratic."[6]
On June 23, spokesman Sawyer reported that Sanford had contacted his staff that morning—after apparently being out of touch with them for five days—and expressed surprise at all of the attention to his absence. Sawyer announced that the governor had decided to return to work the next day.[6]"
http://en.wikipedia.org/wiki/Mark_Sa...marital_affair
It later came out that Sanford used public funds for his trips. As a result he was forced to reimburse the state. So it's a bit more involved than just an affair.