The project is opposed by environmentalists because it will require cutting earth from surrounding hills and filling in the canyon with more than 2 million cubic yards of dirt, the newspaper reported.
Elsewhere along the U.S.-Mexico border, fence construction has ranged from around $2 million to a little more than $3 million per mile, according to the Union-Tribune, which also reported that the Smuggler's Gulch fence will stretch for around 3.5 miles.
"Certainly in some areas, it is easier to construct than it is in others," Barry Morrissey, a spokesman for the U.S. Customs and Border Protection, told the newspaper. "Just based on the geography there, this particular segment posed some unusual challenges."
Once completed, the new 3.5-mile stretch of fencing across Smuggler's Gulch will connect with other new fencing in the area to form a 14-mile line of continuous fencing running inland from the Pacific, the newspaper reported.
Several environmental groups, including the Sierra Club and the San Diego Audubon Society, filed a lawsuit in 2004 to block the project, but the action was trumped by federal legislation that gave the Department of Homeland Security the authority to waive all laws and litigation standing in the way of fence construction.