A fire that broke out around the time of impact was out when firefighters arrived, he said.
The Mustang was off the ground when it slammed into the tree on the passenger side, according to reports from the scene.
McKeown said it had to be stabilized before firefighters could get to the victims, who were pronounced dead at the scene. The victims were identified as 18-year-old Mark Motley and 17-year-old Zac Rafferty.
The crash is suspected to have been caused by "high speed and inexperience," California Highway Patrol Officer Eric Barnard said investigators interviewed some witnesses.
The CHP is also looking into whether anyone was racing on the two-lane road.
"It's a possibility," Barnard said, adding that every avenue will be looked into.
The road "is surrounded by oak trees," Barnard said. "It's a popular road for young drivers."
Many students in South Orange County are on spring break, Barnard said.
Several teens, some crying, and distraught family members of at least one victim began gathering at the site by later in the afternoon, Barnard said.
One victim was said to be a student at /*Saddleback High School*/ and the other at /*Santa Margarita High School*/, according to reports at the scene.
Barnard asked that anyone who saw vehicles going at a high speed in the area at the time of the crash to call the CHP's San Juan Capistrano office at (949) 487-4000, or CHP dispatch at (949) 559-7888.
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