Officials in Pomona, California, had to issue an apology after a recreation guide mailed out by the city reportedly included adult content.

“The City of Pomona is aware that some copies of the recently mailed Recreation Guide may include inappropriate images that should not have appeared in a publication distributed to residents,” the city wrote on its Facebook page on Monday.

Officials said that the materials had not been approved for inclusion in the mailer and assured residents that the images were not meant to be included.

According to the Los Angeles Daily News, the images were “pornographic” in nature.

“We sincerely apologize to our community, especially to families and children who may have been affected,” city officials wrote. “This content does not reflect the City’s values, and we take this matter very seriously.”

The city pulled the guide from further distribution and has launched an investigation into how the images wound up in the guide.

Pomona Assistant City Manager Mark Gluba told The Daily Bulletin that officials have confirmed that the images were not added by the print shop the city contracted to produce the physical guides.

He told the paper on Tuesday that the city was “awaiting the Pomona Police Department to come take a crime report and coordinate the investigation in conjunction with the US Postal Inspection Service.”

“Our Community Services Department coordinates the Recreation Guide and approval of the final proof. Per our vendor, US Printing, the errors did not originate from their print shop, thus the City is looking into the matter with the assumption that a rogue actor may have created and mailed the inappropriate material.”

Officials assured the public that they were taking steps to make sure a similar situation does not occur in the future.

“We recognize this incident has damaged public trust and are committed to transparency as we review the issue and implement corrective actions,” city officials wrote.

Residents who want to see the city’s recreation guide as it’s intended to be seen can do so on the city’s website.