There are a plethora of historic places that are so hallowed and so ingrained into the American cultural landscape that any threat to them — be it development, natural disaster or simply the ravages of Father Time — might come across as ludicrous. In the minds of many, these places are simply untouchable.

But as the National Trust for Historic Preservation is here to remind us once again, even America's most storied architectural and cultural sites, many of them enjoying historic landmark protections, can indeed come under threat.

After taking a year off to celebrate 11 preservation success stories, the National Trust has returned to sound the alarm bells with its annual 11 Most Endangered Historic Places list. And like with past editions, a couple particularly iconic — and seemingly invincible — locales have made the cut.

Perhaps the most notable inclusion is none other than the Mother Road herself, U.S. Route 66.

Route 66 passing through Daggett, California America's so-called Mother Road has seen better days. (Photo: David McNew/Getty Images)

So how exactly does a historic 2,448-mile highway, portions of which have been designated as a National Scenic Byway, become endangered?

What specific threat(s) does America's most pop culture-famous stretch of asphalt face?

And is Route 66, established in 1926 as a means of linking the American heartland (Chicago) with the Pacific Coast (Los Angeles), really at risk of disappearing?

Considering that Route 66 technically ceased to exist when it was officially removed from the United States Highway System in 1985, the answers to these questions are somewhat complicated. But in summary, yes, historic Route 66, which is already wildly fragmented in places, could one day fade away altogether if appropriate actions — specifically, an act of Congress and a presidential sign-off — aren't taken.

Shuttered cafe Route 66 The interstate highway system has all but made Route 66 obsolete. (Photo: David McNew/Getty Images)

Once romanticized, now a road less taken

Referring to Route 66 as an "internationally significant symbol of our nation's romance with the open road," the National Trust explains that the bureaucratic gears have already been set in motion to declare Route 66 as a permanent National Historic Trail, which, in turn, would "bring national recognition and economic development to the route's historic sites."

The designation would help to bolster the surviving greasy spoon diners, mom-and-pop service stations and small businesses that once lined the highway in great abundance; it would help to keep the neon glowing at kitschy mid-century motor lodges; it would breathe new life into the quirky roadside diversions — cement sperm whales, leering Paul Bunyan statues, artsy car graveyards and all — and detour-worthy architectural landmarks that once defined the Main Street of America but have since disappeared as motorists opt for the quick convenience of the interstate.

Most important, designation as a National Historic Trail would encourage future generations to veer off the interstates and embark on the classic American road trip just like their station wagon-commandeering forebears did way back when.

Wigman Motel, California The Wigwam Motel, built in 1949, is an enduring Route 66 staple in San Bernadino, California. (Photo: David McNew/Getty Images)

Even further back, Route 66 served as the primary artery for the great westward migration of the 1930s, an event that saw thousands upon thousands of Dust Bowl farmers — the "Okies" of "Grapes of Wrath" fame — load their families into jalopies for the long and arduous trek from the Southern Plains to California in search of a better, more prosperous life.

This all being said, much of historic Route 66 is already lost. This new — and much needed — push by the National Trust seeks to save what's left.

A 'vital preservation opportunity' hangs in the balance

For the designation of Route 66 as a National Historic Trail to move forward, the Senate must pass the appropriate legislation. This would then need to be signed by the president. All of this needs to happen by the end of the year or "a vital preservation opportunity may be lost" per the National Trust. The clock is ticking.

In 2017, the Associated Press reported that Route 66 preservationists are anxious about the future — particularly future federal funding — of the beloved road under the Trump administration. Funding under the current, soon-to-expire preservation program, the Route 66 Corridor Preservation Program, has helped to finance various restoration projects along the route including spiffed-up neon motel signs in New Mexico and rehabilitated gas stations in Kansas. Kaisa Barthuli, program manager for the National Park Service-administered program, tells the AP that $20 million in funding for nearly 150 preservation projects along Route 66 has been distributed along with $3.3 million in matching funds.

These projects have helped to revive tourism along the historic route. In addition to nostalgia-seekers and wanderlust-y Millennials, foreign tourism, which is already believed by some to be in a slump under Trump, is particularly vital to the small businesses scattered along Route 66. The appeal of Route 66 to foreign visitors is strong: the varied landscapes and kooky roadside architecture provides a singular slice of Americana romanticized the world over.

Route 66, New Mexico Route 66 passes through central New Mexico as it links California with the Midwest. (Photo: Robyn Beck/AFP/Getty Images)

(The highway is somewhat of a mixed bag when it comes to political affiliations. The historic route's termini are in the solidly blue states of California and Illinois. Save for New Mexico, every state in between — Missouri, Kansas, Oklahoma, Texas and Arizona — went to Trump in the 2016 presidential elections. Arizona, New Mexico, Missouri and Illinois are all home to sections of the National Historic Byway better known as Historic Route 66.)

However, as an optimistic Guardian points out, a bill that aims to preserve and protect Route 66 is "something surely everyone could get behind in these divided days."

To keep up the pressure as the summer travel season kicks into high gear, the National Trust, working alongside the Route 66 Road Ahead Partnership and various local and state agencies, has launched a petition imploring all Americans to voice their support for the designation of Route 66 as a National Historic Trail. There's also the National Trust's just-launched Route 66 Road Trip, a storytelling-driven five-week journey along the entire route that aims to "capture the spirit of Route 66 and share it with travelers old and new, real and virtual — anyone who dreams of the open road."

Cadillac Ranch, Texas Cadillac Ranch has been luring motorists off Route 66 in Amarillo, Texas, since 1974. (Photo: Robyn Beck/AFP/Getty Images)

A 'slow-burn' threat

As reported by the Chicago Tribune, this is actually the second time that Route 66 has appeared on the National Trust's Most Endangered Historic Places list, which is now in its 31st year.

In 2012, a small segment of the historic highway was listed as being under-threat. But as Amy Webb, senior field director for the National Trust's Denver office, explains to the Tribune, this year's larger inclusion is both more urgent and expansive considering that imminent expiration of the Route 66 Corridor Preservation Program. The program was originally envisioned as a 10-year designation, and has been expanded in the past. Come 2019, however, there will be no opportunity to expand the program, thus the push for National Historic Trail designation.

A bipartisan 2017 bill introducing such a designation authored by Rep. Darin LaHood, a Republican congressman — and the son of former U.S. Secretary of Transportation Ray LaHood — representing Peoria, Illinois, has already gained House approval. In an ideal world, Senate approval and a signature from Trump will follow in quick procession — the quicker the better.

Abandoned Route 66 cafe, Illinois Decrepit roadside cafes such as this one in Litchfield, Illinois, are ripe for a revamp. (Photo: Robyn Beck/AFP/Getty Images)

"The reason we decided this year to list the entire route is that, in addition to losing little parts of the historic interest here and there, is a very specific threat right now," Webb tells to the Tribune. "The best alternative would be to try to have it added as a National Historic Trail. That's designated by an act of Congress, so it's no small lift."

If things pan out the way preservationists and Route 66 boosters hope they do, Route 66 would become the country's 20th National Historic Trial. Others include the Trail of Tears, Alaska's Iditarod, the Pony Express and the path of the three Selma-to-Montgomery civil rights marches held in 1965.

"They aren't necessarily trails, as in, backpacking. Originally they were the roads or the means of travel of their day," Webb elaborates. "The Oregon Trail, the Lewis and Clark Trail — what they had for the time, just like Route 66 before the expressways that eventually replaced parts of it."

Santa Monica Pier and end of Route 66 Route 66 stretches right to the Pacific, terminating at the Santa Monica Pier. (Photo: Frederic J. Brown/AFP/Getty Images)

Webb goes on to tell the Tribune that the threat to Route 66 can be classified as a "slow-burn" that's been continuously unfolding over the decades. As small businesses along the decommissioned route continue to be relegated as irrelevant, time-wasting detours and are eventually forced to shutter, "authentic elements" of the old Route 66 become lost forever.

"People have this vision of taking the iconic road trip along Route 66, and it would be a shame if they did only to find too many places were lost and can't be revitalized," says Webb.

Endangered places from Omaha to Annapolis to East L.A.

Because of the time-sensitive nature of the threat against Route 66 along with the wide geographic scope involved, it's undoubtedly the headline-grabbing entrant in the 2018 Most Endangered Historic Places list.

However, the 10 other sites that make up the most-endangered list (plus one area placed on "watch status") are worth learning more about.

Bagdad Cafe, California Bagdad Cafe, a Route 66 institution in the Mojave Desert, is open for business. (Photo: Gabriel Bouys/AFP/Getty Images)

One, Mount Vernon, is also quite famous. George Washington's sprawling — and hugely visited — riverside plantation is under threat from the potential development of a view-obstructing gas compressor station planned to be built adjacent to nearby Piscataway National Park, which is also classified as endangered by the National Trust.

Of incalculable importance is the protection and preservation of the thousands of hurricane-battered cultural and historic resources found throughout Puerto Rico and the U.S. Virgin Islands. "With another hurricane season already here, recovery efforts for these historic properties continue to face significant challenges due to limited materials, financing, and preservation expertise," writes the National Trust.

In Vermont's Upper Valley, four sleepy rural hamlets — Royalton, Sharon, Strafford and Turnbridge — has been placed on "watch status" due to plans for a futuristic "mega-utopia" in the area being helmed by a wealthy Mormon real estate developer. (These ambitious and hugely contentious plans seem to have unraveled in recent days as the developer in question has announced he is throwing in the towel after being worn down by "the drama" surrounding his Joseph Smith-inspired mini-city.)

City Dock, Annapolis Annapolis' historic City Dock was also named one of America's most endangered places for 2018. (Photo: Mike Boswell/flickr)

Other historic sites being threatened by development include the Colonial-era City Dock in Annapolis, Maryland, Denver's Larimer Square and the Ashley River Historic District in Charleston, South Carolina.

Rounding out the list is the Dr. Susan LaFlesche Picotte Memorial Hospital on Nebraska's Omaha Indian Reservation; the Isaiah T. Montgomery House in Mound Bayou, Mississippi, and the Mary and Eliza Freeman Houses in Bridgeport, Connecticut, both significant African-American historic sites; the Wallace E. Pratt House (aka Ship on the Desert), a landmark Modernist home within Guadalupe Mountains National Park in Texas; and the Walkout Schools of East Los Angeles (James A. Garfield High School, Theodore Roosevelt High School, Abraham Lincoln High School, Belmont High School, and El Sereno Middle School), all of which played a central role in the Chicano Civil Rights Movement.

No doubt being named one of America's Most Endangered Historic Places can be dispiriting. But in the end, inclusion on the list serves as more of a call to arms than a death rattle — earning a not-so-coveted spot on it tends to bolster protections of a vulnerable site, not hasten its demise. Of the over 300 historic places that have been classified as endangered by the National Trust since the inception of the program in 1988, less than 5 percent of them have been lost for good to deterioration, decay or new development.

Here's hoping that the road is smooth for Route 66 and other historic sites in the uncertain months ahead.

Matt Hickman ( @mattyhick ) writes about design, architecture and the intersection between the natural world and the built environment.

Why Route 66 is on the list of America's most endangered places
The fabled highway's inclusion on the National Trust for Historic Preservation's annual most endangered list might come as a surprise .