By Liam Dillon
The sidewalks in parts of mid-city never had a chance.
That’s according to Leslie Reed, the founder of local engineering firm Geotechnical Exploration. More than two decades ago, he wrote a paper deeming the land in and around Normal Heights the worst surface to build on in San Diego. He called the problematic material Normal Heights mudstones.
“They’re so explosive, so expansive, it’s very difficult to figure out what to do with them,” Reed said.
These mudstones wreak havoc on homes, commercial and retail buildings, streets and sidewalks, Reed’s research found. When wet, the steely gray dirt feels like the spongy modeling clay popular in elementary school classrooms. But when it dries, it crumbles into tiny pieces.
Over time, Normal Heights mudstones can lift building foundations off the ground, causing potentially hundreds of thousands of dollars’ worth of damage to homes, Reed said. Something as simple as a poor parallel parking attempt could be enough to ruin a curb built on top of Normal Heights mudstones.
It’s this land, not the age of City Heights, Normal Heights and North Park, that explains why older, central San Diego neighborhoods have such poor sidewalks, Reed said. He works in other neighborhoods just as old that don’t have the same problems.
A map detailing the concentration of Normal Heights Mudstone. The material can be found under streets and sidewalks in the Corridor, Teralta and Fairmount neighborhoods. | Illustration Courtesy of Leslie Reed
The city is aware of the Normal Heights mudstones as well as deposits around Pacific Beach, Otay Mesa, Kearny Mesa and others, said Bill Harris, a transportation department spokesman. He’s not as convinced that mudstones play the defining role in crumbling sidewalks. Age, material quality and other development conditions matter just as much, he said.
“It’s a contributing factor,” Harris said. “It’s not the reason.”
These days, Harris said, the city removes or compacts mudstones before it builds anything.
Reed has the same advice. Below Normal Heights mudstones sit sandstone, some of the best land for building. But getting rid of the mudstones isn’t easy. In certain locations in Normal Heights, Reed found, mudstones go down more than 13 feet.