Federal Aviation Administration spokesman Ian Gregor says rescuers were attempting to hike to the wreckage Sunday. The fate of the passengers is unknown.
A Mexican military helicopter spotted the wreckage of the Beechcraft Baron in steep and rugged terrain near Cabo San Lucas on Saturday. They were unable to land.
Mexican officials said they believe four people were aboard.
Gregor says the plane is thought to have departed from San Diego to Los Cabos, Mexico, en route to Argentina.