The San Antonio Missions National Historic Park is fighting for a $236,000 grant to preserve historic frescoes, and only your votes will help procure the cash.

The #VoteYourPark contest is offering a six-day trip to Jackson, Wyo., and Yellowstone National Park in exchange for votes for preservation projects at 20 National Parks. One voter will get the grand prize, provided by National Geographic.

But the big winner, the contest suggests, will be the parks that split a $2 million prize for their projects. To get the check, however, the parks have to win the #VoteYourPark digital poll.

This is the eighth time that Partners in Preservation -- a collaboration of American Express and the National Trust for Historic Preservation -- has funded projects through an online poll, said spokesman John Hildreth, but the first time the grants have gone specifically to National Parks.

The National Park Service is celebrating its centennial this year, so the groups worked together to highlight not only the well-known parks like Yellowstone and Yosemite, but also smaller parks like Minute Man National Park in Massachusetts.

"This was a way for us to share the breadth of what our national park system represents," Hildreth said. "This helps raise visibility."

Each participating park — there's 20 of them from Denali in Alaska to the missions in San Antonio — has already received $100,000 to help spread public awareness about their proposed projects. At the end of the voting period on July 5, the top vote-getters will be funded.

As of midday Friday, Great Smoky Mountains National Park is in the lead with a $250,000 project to restore Clingmans Dome Observation Tower. No surprise there, as it is the most popular park in the country. Rounding out the top five are Yellowstone National Park, Grand Canyon National Park, Yosemite National Park and World War II Valor in the Pacific National Monument in Pearl Harbor, Hawaii. The San Antonio Missions project is in 13th.

Here's the full list of participating parks. Vote online at nationalgeographic.com/voteyourpark.