The USGS conducted surveys of the Fire Island National Seashore along Long Island using light detection and ranging lasers to examine elevation changes in dunes.
Cheryl Hapke, a coastal geologist, said Sandy caused widespread dune erosion at the park.
"On average, where the dunes were not completely overwashed, they eroded back 70 feet -- the equivalent of 30 years of change," she said in a statement. "Our research also showed that dunes lost as much as 15 feet of elevation."
Sandy hit the U.S. East Coast late October as a Category 1 storm. It merged with an eastward-bound storm system, creating a so-called superstorm.
USGS Director Marcia McNutt said dune systems provide a natural defense for storms like Sandy.
McNutt said this month the amount of wave erosion caused by the hurricane reached historic proportions.