10.5

Part 1[edit]
The film begins in the Seattle, Washington area with increasingly severe earthquake activity. A quake of magnitude 7.9 is measured at the Earthquake centre, where Dr. Samantha Hill takes command, displacing Dr. Jordan Fisher. U.S. President Paul Hollister and FEMA Director Roy Nolan are informed about the situation.
A magnitude 8.4 earthquake opens a crack which engulfs a train east of Redding, California. As a result, Governor Carla Williams, who had just seen her daughter and ex-husband off on a camping trip, agrees to help the Governor of Washington. Amanda Williams and her father Clark Williams arrive at a town named Browning, where everything is covered in a thick red haze. They discover a car with a dead family inside, and are nearly trapped in quicksand.
Roy Nolan constructs a task force of the best geologists and seismologists, including Dr. Fisher and Dr. Hill. Dr. Hill mentions her Hidden Fault theory, and is eventually given permission to prove it. She and Dr. Fisher visit a lake, where they see some animals that died from carbon monoxide poisoning, and are almost poisoned themselves.
Back at the Task Force Center, Dr. Hill predicts that the next quake will be near San Francisco, California. It is deemed too risky to evacuate the entirety of San Francisco, which is eventually destroyed by a 9.2 magnitude earthquake. After that Dr. Hill predicts the next quake will happen at the San Andreas fault, which would wipe out the West Coast in its present shape killing 50 million people on the way. Dr. Hill hypothesizes that they could "weld" the fault shut by letting it experience immense heat, which could only be created with nuclear bombs.
Part 2[edit]
The President after some deliberation follows Nolan's advice to execute Dr. HillÂ´s plan and allows the placement of the nuclear warheads. Additionally he gives the order to evacuate the entire West Coast in case it fails and mobilizes all resources available for it.
Five of the six nuclear bombs have been successfully installed, but during the installation of the sixth an earthquake occurs, and a warhead is lost. Nolan tries to set it manually, but is pinned by the warhead.
The Williams find a truck carrying survivors, and they are transported to Tent City, which has been set up for the refugees. In a wounded San Francisco, Carla Williams and her assistant Rachel are trapped under a wall. Carla survives, but Rachel is killed.
Deciding that nothing can be done about the lost sixth warhead, Dr. Hill decides to continue with the fault welding plan and detonate the first five. The sixth is activated by Nolan who manages to reach the control panel just in time, but is himself incinerated.
It seems to work, until Dr. Hill, concerned about southern California, observes a river flowing backwards, draining into the open fault. The last warhead was not deep enough when it exploded and Southern California is still in danger. Shortly after, a massive earthquake occurs. Eventually the crack reaches Tent City and peaks at 10.5. When the earthquake stops, the survivors see that the southwestern coast of California has been cut away, forming a new island.

Question: What are Carla and Rachel trapped under?
Answer: wall