SAN ANTONIO -- With about 30,000 registrants, Sunday morning's Rock 'n' Roll Marathon is being billed as the single largest inaugural marathon in United States history, event organizers said.

Hotel rooms across the city are booked solid as more than two-thirds of the registrants are from outside the city, said Richard Perez with the San Antonio Chamber of Commerce.

"My wife and I tried to get a hotel downtown so we could be closer to the starting line and we couldn't find a hotel," he said. "We started a month ago."

Race organizers said they try to find locations that welcome tourism, so San Antonio was "a no-brainer," said event organizer Bruce Perry.

"We like San Antonio because it's a really fantastic destination, and our business is to try to get people from all over the country to come to these events, not just local people, and San Antonio is the number one tourist destination in Texas, and it has a great reputation for that," he said.

Perez said the economic impact of the marathon will rival other major events in terms of money spent across the city.

"We're talking restaraunts, we're talking shopping, we're talking clothing," he said. "I mean, it does it all."

Participants and fans are being forewarned to check traffic levels Sunday morning, as various downtown streets will be closed for the race. A copy of the route map (PDF) shows the various streets being affected by the race.