"Ghost Country" by Patrick Lee
Second novel by Lee about "The Breach", the tunnel (wormhole?) buried under ground that spits out fantastic artifact from the future (many of which are useless). In this second book, Travis Chase, after walking away from Tanget (the secret organization overseeing the Breach) and his lover Paige Campbell, is living alone under a new identity when Bethany Stewart, Paige's colleague, arrives on his doorstep asking for help finding Campbell. Campbell had just shown the President a new artifact, and after the meeting Cambell's motorcade was attacked, with everyone killed but her.
Stewart has the twin of the object, a cylinder that she and Chase discover will open a portal to approximately 70 years into the future. The future they find is one where apparently civilization has fallen, with humanity dead. Thus begins a race to fist rescue Campbell, and then discover what happens in the next few month that kills off humanity.
Given that Lee had already introduced the Breach in his first novel, the big SF idea here is one involving ELF (extremely low frequency) radio waves, and their possible effect on human health and emotion. This, along with the portal to the future, and the conspiracy that involves a lot of the movers and shakers in the US (along with the President) is a lot to juggle, but Lee handles it pretty well. I think he's very adept at handling action scenes, and one of the highlight is a major action scene in abandoned Yuma, AZ, among a sea of parked cars that have been sitting for 70 years.
A nice read, and it certainly leaves the door open if he wants to continue writing in this universe.