The plodding lines some Salt Lake County voters found themselves in late Tuesday coupled with the last-minute mail-in ballots inundated the county clerk’s office, which still had more than 100,000 ballots to process by Thursday evening, according to Salt Lake County Mayor Ben McAdams.

The reason? A “perfect storm,” he said.

“There were a lot of people saying they didn’t trust putting their ballot in the mail would get it counted,” McAdams added.

Lt. Gov. Spencer Cox said Utah—for the first time in decades deemed a swing state—saw a rush of late-game registrations. On the final days to register, an unprecedented 50,000 residents signed up for the election, “most of them were in Salt Lake County,” he said, but too late to grab a mail-in ballot. This added to the influx the county hadn’t anticipated.

In addition, Salt Lake County was one of eight counties in the state that allowed same-day registration. About 10,000 people chose that option, Cox said, which slowed down the lines because it is relatively time-intensive.

McAdams and Cox spoke on Thursday evening at an event hosted by Utah Foundation, a nonprofit policy think tank.