Fort Jefferson at Dry Tortugas National Park needs roughly $41 million in masonry work/NPS

As Congress works in the coming months to reach accord on legislation that would provide billions of dollars to address the National Park System's nearly $12 billion in maintenance work that's been put off for a year or longer, the backlog continues to inch higher and higher.

If a funding mechanism is passed, then the National Park Service will have to craft, annually, a national priority list of projects that need to be tackled. While that list doesn't exist yet, here's a look at some possible top priorities based on projects pending at the end of Fiscal 2017, last September 30.

* The East Potomac Park Seawall, National Mall & Memorial Parks

A protective barrier to keep the Potomac River in its place, the seawall carries a $253.9 million deferred maintenance backlog, and a current replacement cost of $363.3 million. The Park Service gave it a "high" priority ranking and a "high" visitor value.

* Trans-Canyon Water Pipeline, Grand Canyon National Park

The need to replace this pipeline that brings water from the North Rim to the South Rim long has been known. Park officials currently are exploring the best way to do that. The deferred maintenance price tag is $119 million, but the current replacement value is pegged at $437.5 million. The Park Service deemed it to rank "high" on its value to visitors.

* The Jacob Riis Parking Lot at Gateway National Recreation Area

This lot carries a $181.4 million deferred maintenance cost, which exceeds its current replacement value by roughly $31 million.

* Roads at Colonial National Historical Park

There is about $67 million in overdue maintenance on this park's road system; current replacement costs approach $208 million.

* Roads in Yellowstone National Park

Current deferred maintenance runs to $64 million, though current replacement value is $93.2 million. That figure could grow once the park staff figures out how best to replace the Lewis River Bridge.

* The Blue Ridge Parkway

Maintaining the parkway's roads are the biggest expense in this park, representing $54.2 million in deferred maintenance. Current replacement value is nearly three times that, $149 million.

* Concessions buildings, Yosemite National Park

The park's concession facilities carry $52.5 million in deferred maintenance, which would balloon to $310 million if a decision was made to simply replace the buildings.

* Natchez Trace Parkway

This ribbon of highway has $48.2 million in deferred maintenance needs, which would cost $80.8 million if the roads were built anew.

* Trails in Mammoth Cave National Park

Though the park's main attraction is underground, the above-ground trails system needs $42 million worth of work.

* Fort Jefferson, Dry Tortugas National Park 

This 19th century fortress has been battered by hurricanes and time; its masrony needs represent $41.3 million in deferred maintenance. Think it'd be better to simply replace the fort? That would cost about $1.3 billion, according to Park Service estimates.

* Statue of Liberty National Monument.

The monument's waterfront carries more than $38 million in deferred maintenance, work that would cost $233.3 million if the waterfront was built from scratch today.

* Gulf Islands National Seashore

Fortifications at this seashore have a deferred maintenance list that runs to $36.3 million; current replacement value would be more than $153 million.