NEW YORK (AP) - If you're thinking about a trip to a national park next summer, you may want to start researching your itinerary now.

Campsites and cabins can be secured up to six months in advance at http://www.recreation.gov and the National Park Service has a wealth of free information online for individual parks.

If you're looking for a guidebook, Fodor's is out with its 13th edition of "The Official Guide to America's National Parks" ($18.95), with listings for 391 national parks, including scenic trails, battlefields and other historic sites.

The book is organized by state, but also includes sections on U.S. territories in American Samoa, Guam, the Virgin Islands and Puerto Rico, where the San Juan National Historic Site preserves Spanish colonial fortifications dating to the 16th century.

The book also includes listings by category to help you find parks related to special interests.

For example, a list of African-American history sites inc ludes the Brown v. Board of Education National Historic Site in Kansas, the Martin Luther King Jr. National Historic Site in Georgia, the George Washington Carver National Monument in Missouri, Harpers Ferry National Historic Park in West Virginia, New Orleans Jazz National Historical Park in Louisiana, the Tuskeegee Institute National Historic Site in Alabama and the Frederick Douglass National Historic Site in Washington D.C.

There are also listings for sites related to archaeology and paleontology, battlefields, Civil War, Hispanic heritage, women's history, presidential history sites and volcanoes, caves and hot springs.

Copyright 2008 The Associated Press.