A car was found buried Thursday in the yard of a home in the affluent town of Atherton in the San Francisco Bay Area, police said.

Landscapers working in the yard discovered the car around 8:50 a.m. It had been buried below 4 to 5 feet of dirt and was thought to have been there since the 1990s, police said.

How it got there and why it was there was under investigation. The vehicle was being excavated Thursday.

Cadaver dogs were brought in and “made a slight notification of possible human remains,” police said in a statement.

No human remains have been found, Atherton police Commander Dan Larsen said late Thursday.

There were unused bags of concrete in the vehicle, police said.

“The motive and circumstances surrounding this incident are under investigation,” police said in a statement.

The vehicle is not associated with the current homeowners, and was buried before they moved in, police said.

Atherton is a wealthy community in San Mateo County. The city of around 7,100 is adjacent to Menlo Park, home of the headquarters of Facebook’s parent company Meta, and less than 10 miles from Mountain View, where Google is headquartered.

Atherton was ranked as the nation’s most expensive ZIP code for a fifth consecutive year last November, according to real estate information company PropertyShark. It had a median sale price of $7.5 million.