When you're at an airport, most likely you're caught up in the frenzy of your trip - rushing to make it to the gate in time, hoping that you didn't forget anything, re-playing the itinerary of your trip in your head.  But next time you visit one - there's something else to consider - the history of your airport. Some U.S. airports have very compelling, non-aeronautical pasts. USA Today uncovered some interesting details about some of our airports, dating back decades - and even centuries - before planes took off and landed there.

At Seattle-Tacoma International Airport, there's evidence that large creatures roamed the land now occupied by Seattle-Tacoma International Airport. In Feb. 1961, a construction crew working in a bog along an airport runway came across the bones of a 12-foot-long sloth, or Megalonyx, apparently over 12,500 years ago. The sloth was only missing a skull and some neck and limb bones, so another complete Sea-Tac sloth skeleton was created with casts taken from another Megalonyz specimen - now on display at Seattle's Burke Museum.

Denver's International Airport may have been in a subtropical climate years ago, judging from fossils of palm leaves that workers found in 1992 when they dug up earth to make way for Concourse B.

"In the historical timeline, the prairie where Denver International Airport was built was most recently farmland," airport spokesperson Laura Coale told USA Today. "Some original homesteading families still cultivated winter wheat, sunflowers and other crops," and today some airport-owned land is still used for farming.

Other airports, such as Fresno Yosemite, Dulles and Miami International Airport used to be undeveloped agricultural or scrub land. San Jose International Airport used to be an onion field, and Los Angeles International Airport was home to former bean fields.

"Farmland was ideal for airports because the land had already been tilled and cleared of trees and, in the very early days of aviation, you didn't need such a long runway to take off," F. Robert Van Der Linden, chair of the aeronautics department of the National Air and Space Museum at the Smithsonian Institution, told USA Today.

World War II allowed many modern-day airports, including Orlando International to get their start, Van Der Linden told the paper. "We covered the country in airfields for military training purposes," he said. Many such airfields were later turned over to local governments and then transformed into commercial airports.

Washington Reagan International Airport was "constructed on landfill," not far from a former colonial plantation known as Abingdon, Rob Yingling, Metropolitan Washington Airports Authority spokesperson told USA Today. "But before it was an airport, it was the Potomac River."

Other airports have speedway pasts -- like Minneapolis-St. Paul, built on the site of the Snelling Speedway. "The airport was initially known as Speedway Field in reference to its auto racing history," airport spokesperson Patrick Hogan told USA Today, "and in early photos you can still see the oval outlines of the former auto raceway surrounding the airport."

In 1925, the Atlanta mayor signed a lease committing the city to developing an airfield on an abandoned auto racetrack - which ultimately became the Hartsfield-Jackson Atlanta International Airport. "The infield of the old racetrack had been used as a landing site for many years prior to 1925," the airport's website notes.

The John Wayne Airport (SNA) in California's Orange County used to be a private landing strip in the 1920s established by aviation pioneer Eddie Martin. In the 1950s, its runway doubled as a Santa Ana Drug Races speedway.

Golfers used to tee up on the grounds of some current airports. Fort Lauderdale-Hollywood International Airport (originally the Merle L. Fogg Airport) opened in 1929 on the site of a municipal golf course that closed a year before. According to the history section of its website, "only a minimal amount of work was needed to convert it into an airport. Trees and bushes were cleared from the perimeter of the course and its bunkers were leveled. Its unpaved runways were the former fairways suitable for the planes of the day."

Norfolk International Airport (ORF), turning 75 this year, moved in 1938 to what used to be the Truxton Manor gold course.  Its first terminal building  "had either been the pro shop or the caddy shack at the golf course," Charles Braden, director of market development for the Norfolk Airport Authority, told USA Today.

In New York, LaGuardia Airport used to be home to an amusement park. John F. Kennedy Airport also had a golfing past - in 1963, the city turned Idlewild Golf Course into Idkewild Airport.

At Savannah/Hilton International Airport, pilots and passengers occasionally spot grave markers along the runway.

In the late 1800s, some members of the Dotson family were buried in a remote private clearing in the woods. In the 1970s, those graves ended up in the path of a planned airport runway expansion.

Although the caskets and their caskets are long rotted away, the grave markers are still there. ""The airport had power of eminent domain [to take the land and move the markers], but there could have been a court battle," said Patrick Graham, the executive director of the Savannah airport commission, to USA Today.

The airport and Dotson family descendants agreed that although the markers for the deceased would be surveyed and removed during runway construction, they would be returned to their spots - luckily not on the center of the runway -- once the work was completed.

"Planes aren't rolling over them," Graham told USA Today. "We are probably the only airport with gravesites that close to the runway," said Graham. "But it is in keeping with and respectful of the family's wishes."