Update, March 25: President Obama officially designated five new national monuments Monday afternoon in a signing ceremony at the Oval Office.

"These sites honor the pioneering heroes, spectacular landscapes and rich history that have shaped our extraordinary country," Obama said in a statement. "By designating these national monuments today, we will ensure they will continue to inspire and be enjoyed by generations of Americans to come."

Read more about each of the new national monuments below:

President Obama is expected to designate five new national monuments Monday, including two natural Western landscapes, two historic sites dedicated to pioneering African-Americans, and the first-ever National Park Service unit in Delaware.

"President Obama has taken an important step in protecting America's outdoor heritage and honoring our nation's history," said Brian O'Donnell, executive director of the Conservation Lands Foundation, in a statement released Friday. "These designations came in response to locally driven efforts and we are grateful for President Obama's leadership in advancing conservation at a time when it's desperately needed."

The Antiquities Act of 1906 lets the president make such designations without congressional approval, a power Obama scarcely used in his first term. Some Republican lawmakers have called for repealing the law, but former Interior Secretary Bruce Babbit recently chastised Obama for "making concessions" and not aggressively protecting natural and historic landmarks. "The best defense of the Antiquities Act is to use it," Babbit said last month at the National Press Club. "And the reason for that is by using it, we show the American people what we have and what the program is for protecting it."

Here are the five national monuments Obama is expected to christen Monday:

San Juan Islands National Monument, Wash.

Sunset at Guemes Island, San Juan Islands, Wash. (Photo: docentjoyce/Flickr)

Located between Washington state and Canada's Vancouver Island, the San Juan Islands are famed for their natural beauty and ecological diversity. The archipelago consists of 172 islands, ranging from tiny rocks to half-mile-high mountains, and has some 300 miles of shoreline. It's home to an array of wildlife, including bald eagles, bluebirds, black-tailed deer, orcas and otters. Tourism is a major industry on the islands, with visitors flocking there for hiking, fishing, kayaking, whale-watching and many other activities.

Rio Grande del Norte National Monument, N.M.

The Rio Grande meets the Red River in northern New Mexico. (Photo: Adriel Heisey)

Carved into northern New Mexico by its namesake river, the Rio Grande del Norte region includes landscapes ranging from the 10,000-foot-high Ute Mountain to the 200-foot-deep Rio Grande Gorge. Conservationists have long pushed for more protection of the area, citing its scenery as well as its ecological and historical importance. "Many generations have enjoyed and lived off this landscape, and today President Obama has ensured the local community that this special place will stay as it is for our children, grandchildren, and those who follow," John Olivas of the New Mexico Wilderness Alliance says in a statement.

First State National Monument, Del.

The Green in historic downtown Dover, Del. (Photo: Mr. T in D.C./Flickr)

Delaware is the only U.S. state with no National Park Service units, which is odd since it's the first U.S. state. But that's about to change, thanks to the First State National Monument, a group of four historical sites including the Dover Green Historic District (pictured above), the Woodlawn Trustees property near Wilmington, the Old New Castle Courthouse and the New Castle Green. While state leaders still want a national park, many nonetheless applaud the new national monument. "A national designation will draw more people to discover the stories in our history and landmarks of early settlers here in the First State," Gov. Jack Markell says in a statement. "This marks a first for Delaware and helps put us on the map for visitors, history buffs and park enthusiasts everywhere."

Charles Young Buffalo Soldiers National Monument, Ohio

The Colonel Charles Young House, built in 1864. (Photo: Nyttend/Wikimedia Commons)

Born in 1864 to former slaves, Charles Young attended the U.S. Military Academy at West Point and was just the third African-American cadet to graduate and become an Army officer. He led the legendary Buffalo Soldiers during a 37-year military career, serving a variety of assignments in the U.S., the Philippines, Haiti, Liberia and Mexico. He was also the first black man to receive the rank of colonel, and even served as acting superintendent of Sequoia National Park more than a decade before the NPS was established. And thanks to the creation of the Charles Young Buffalo Soldiers National Monument, the NPS will now protect and maintain his home in Ohio.

Harriet Tubman and the Underground Railroad National Monument, Md.

The Harriet Tubman Centennial Commemoration on March 9, 2013. (Photo: MDGovPics/Flickr)

Harriet Tubman was a pioneer of human rights in America, serving as "conductor" of the Underground Railroad — a network of safe houses that helped African-Americans escape slavery — and later as an advocate for women's suffrage. Born into slavery herself in Maryland, she escaped and played a key role in the abolitionist movement, both via peaceful resistance and as a Union spy during the Civil War, when she became the first woman in U.S. history to lead a military raid. To honor her legacy, the NPS will manage the new Harriet Tubman Underground Railroad National Monument, located on Maryland's eastern shore of Chesapeake Bay. According to the Conservation Fund, the land will be "physically and thematically linked to Blackwater National Wildlife Refuge."

The monument will also include the Harriet Tubman Underground Railroad State Park Visitor Center, which was commemorated earlier this month to coincide with the 100th anniversary of Tubman's death. "Harriet Tubman triumphed during a time of great adversity and in spite of her circumstances persevered, not only for herself, but for her family and community," Maryland Gov. Martin O'Malley said in a statement. "Let us build upon her courage to help make our communities stronger and rise up from our struggles."

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Russell McLendon ( @russmclendon ) writes about humans and other wildlife.

U.S. to create 5 new national monuments
The list includes two natural Western landscapes, two sites dedicated to icons of African-American history, and the first NPS unit in Delaware.