That same terrain, in addition to massive landslides and aftershocks from Monday's earthquake, has hindered efforts to reach survivors in two townships, Genda and Wolong, where the majority of homes have been leveled, according to a report from an official from Wolong's captive panda center, which was communicated to USCEF's Chinese staff.
A graduate student from Beijing, who works on ecological issues in Wolong, reported to USCEF's Brody that news relayed via satellite phone suggests the "general status [in the townships] is very serious indeed."
The student said that clean water and medicine are in short supply, with the water supply "paralyzed" in at least one village.
But food is being airdropped now to Wolong, the student added, and medicine will reportedly arrive when Wolong Administrator Zhang Hemin arrives in the region on a military helicopter on Thursday.
Rescuers must enter the area on foot, as a new national highway just built through the Wolong reserve has been mostly obliterated, Brody said.
"The one link between Wolong and the outside world has been sealed off," he said.
Brody, whose USCEF staff are currently the only international group in the Wolong region, said the heaviest devastation and worst human casualties have occurred at the edges of the Sichuan Giant Panda Sanctuary.
"Tragedy has struck hardest in these heavily populated communities close to Wolong and the epicenter," Brody said.
There could be "tremendous loss of life" in the neighboring towns of Yingxiou and Wenchuan, east of Wolong, as well as in Beichuan county northeast of Wolong, he said.
Xinhua reported Wednesday that 7,700 people were killed in Wenchuan, but it wasn't clear if that figure was included in the larger toll of 12,000.
Brody learned Tuesday that 19 villagers near Wolong died when their stone houses collapsed, but there have not been updates since.
The Associated Press contributed to this report.