Sunrise over the Sangre de Cristo Mountains. Great Sand Dunes National Park, Colorado. 2018.

Sunrise over the Sangre de Cristo Mountains. Great Sand Dunes National Park, Colorado. 2018.

Gwynn standing on the edge. Black Canyon of the Gunnison National Park. Colorado. 2018.

Gwynn standing on the edge. Black Canyon of the Gunnison National Park. Colorado. 2018.

Deck of the U.S.S. Arizona, Pearl Harbor National Memorial, Hawaii. 1998.

Deck of the U.S.S. Arizona, Pearl Harbor National Memorial, Hawaii. 1998.

Taking in the view from the south rim of the Chisos Mountains (Photo by Todd Munson). Big Bend National Park, Texas. 2001.

Taking in the view from the south rim of the Chisos Mountains (Photo by Todd Munson). Big Bend National Park, Texas. 2001.

The hoodoos of Wall Street. Bryce Canyon National Park, Utah. 2017.

The hoodoos of Wall Street. Bryce Canyon National Park, Utah. 2017.

Nightly exodus of thousands of Mexican free-tailed bats. Carlsbad Caverns National Park, New Mexico. 2001.

Nightly exodus of thousands of Mexican free-tailed bats. Carlsbad Caverns National Park, New Mexico. 2001.

Toklat River and the Brooks Range. Denali National Park, Alaska. 2007.

Toklat River and the Brooks Range. Denali National Park, Alaska. 2007.

Sunrise in the House of the Sun. Haleakala National Park, Hawaii. 1999.

Sunrise in the House of the Sun. Haleakala National Park, Hawaii. 1999.

Wild flowers in Kilauea Iki Crater. Hawaii Volcanoes National Park, Hawaii. 1998.

Wild flowers in Kilauea Iki Crater. Hawaii Volcanoes National Park, Hawaii. 1998.

Plumbing in the Fordyce Bathhouse. Hot Springs National Park, Arkansas. 2018.

Plumbing in the Fordyce Bathhouse. Hot Springs National Park, Arkansas. 2018.

Flying a kite on the beach. Indiana Dunes National Lakeshore, Indiana. 2002.

Flying a kite on the beach. Indiana Dunes National Lakeshore, Indiana. 2002.

Sunrise over the Mojave Desert. Joshua Tree National Park, California. 2001.

Sunrise over the Mojave Desert. Joshua Tree National Park, California. 2001.

Holgate Glacier entering Aialik Bay. Kenai Fjords National Park, Alaska. 2007.

Holgate Glacier entering Aialik Bay. Kenai Fjords National Park, Alaska. 2007.

Milky Way Galaxy over Wheeler Peak. Great Basin National Park, Nevada. 2017.

Milky Way Galaxy over Wheeler Peak. Great Basin National Park, Nevada. 2017.

The 9:01 Gate, marking one minute before tragedy. Oklahoma City National Memorial, Oklahoma. 2002.

The 9:01 Gate, marking one minute before tragedy. Oklahoma City National Memorial, Oklahoma. 2002.

Petrified tree. Petrified Forest National Park, Arizona. 2002.

Petrified tree. Petrified Forest National Park, Arizona. 2002.

Grove of coastal redwoods. Redwood National Park, California. 2002.

Grove of coastal redwoods. Redwood National Park, California. 2002.

Forest of cactus. Saguaro National Park, Arizona. 2001.

Forest of cactus. Saguaro National Park, Arizona. 2001.

Big sky on trail across plateau. Theodore Roosevelt National Park, North Dakota. 2016.

Big sky on trail across plateau. Theodore Roosevelt National Park, North Dakota. 2016.

Underneath the arch. Gateway Arch National Park, Missouri. 2018.

Underneath the arch. Gateway Arch National Park, Missouri. 2018.

Vulture in abandoned barn. Shenandoah National Park, Virginia. 2014.

Vulture in abandoned barn. Shenandoah National Park, Virginia. 2014.

Gun emplacement on the outer defenses. Valley Forge National Historic Park, Pennsylvania. 2018.

Gun emplacement on the outer defenses. Valley Forge National Historic Park, Pennsylvania. 2018.

Pelican along Waterlemon Bay. Virgin Islands National Park, U.S. Virgin Islands. 1998.

Pelican along Waterlemon Bay. Virgin Islands National Park, U.S. Virgin Islands. 1998.

Wesleyan Chapel, site of first women's rights convention in 1848. Women's Rights National Historic Park, Seneca Falls, New York. 2019.

Wesleyan Chapel, site of first women's rights convention in 1848. Women's Rights National Historic Park, Seneca Falls, New York. 2019.

Scorched earth. Yellowstone National Park, Wyoming. 2002.

Scorched earth. Yellowstone National Park, Wyoming. 2002.

The Valley, during my first visit to a national park as a teen. Yosemite National Park. 1989.

The Valley, during my first visit to a national park as a teen. Yosemite National Park. 1989.