The second-longest river in North America is the Mackenzie, running 1,100 miles through Canada's Northwest Territories to the Beaufort Sea.

It's named for Alexander Mackenzie, a Scottish fur trader and explorer who had hoped it was the Northwest Passage, the long-sought shortcut to the Pacific. In June 1789, the trader and a crew of 13 made up of voyageurs and native peoples pushed their three birchbark canoes off from the Great Slave Lake to follow what the natives called the Deh Cho, into a land unknown to Europeans.

It was a 40-day ordeal that ended in a wall of ice. Instead of flowing west as Mackenzie believed, the Deh Cho turned north toward the Arctic. He could only name it Disappointment River.

In June 2016, Brian Castner pushed his 18½-foot fiberglass canoe into the river at about the same spot where Mackenzie launched, to retrace the path. Castner enlisted three companions who would replace each other at intervals along the route. Instead of animal skins, he filled his craft with "an Everest-rated tent, solar panels and satellite link … ninety freeze-dried dinners."

Since the 2012 publication of his Iraq war memoir, "The Long Walk: A Story of War and the Life That Follows," Castner is building a reputation as a talented nonfiction writer in the mode of Sebastian Junger. His memoir was adapted into a well-received opera and he's published widely in print and online as well as contributing to National Public Radio, reporting from the Middle East and Africa.

His homecoming after three tours as a bomb disposal expert was marked by post-traumatic stress disorder and the estrangement it caused from his wife and children. Why, then, did he leave them again to make this test of endurance?

"My natural writerly inquisitiveness combined with a paddler's desire to explore new waters," he writes. "To enter my own terra nova."

This expedition, funded in part by a grant from the Pulitzer Center, was Castner's opportunity to learn about the 18th-century world of the quest for animal skins that drew many French and British adventurers farther and farther west past Detroit and deeper into an uncharted territory.

Set over two wars, it's a fascinating and little known history of North America, told in the words of Mackenzie's expansive diaries and retold with enthusiasm by Castner. He's a compelling writer with a fluid style that mirrors the smooth passages of his canoe through the Mackenzie.

The author's friendliness and tolerant approach to Canada's native population gives readers a clear picture of the difficult life in the Northwest Territories. Castner also presents a grim picture of the effects of climate change on the far north. He encountered no ice as he paddled into the Arctic.

"Disappointment River" is an adventure tale that will keep you happily reading while safely in your armchair.

Another book of exploration is historian Edward J. Larson's "To the Edges of the Earth," in which he tells the stories of three 1909 expeditions.

There's the Italian nobleman Prince Luigi Amedeo, who launched a few explorations starting in the 1890s, including a failed North Pole effort. The duke finally succeeded somewhat in 1909 by almost scaling Himalayan mountain K2, reaching 24,600 feet.

Englishman Ernest Shackleton, described by Larson as equal parts adventurer and publicity hound, won the support of the king of Great Britain and generous Australians to mount a drive to reach the South Pole. Hardy, but not foolhardy, Shackleton led his men to the farthest point south at 88 degrees, 23 minutes before turning back due to bad weather.

American Robert Peary was the only one of the lot to succeed when he reached the North Pole on April 6, although his African-American expedition member Matthew Henson probably got there first. Peary's triumph was sullied by the claims of another American, Frederick Cook, who claimed he made it to the pole a year earlier. A public tussle ensued with Peary proclaimed the winner; it took the National Geographic Society and an act of Congress to settle the dispute.

Larson writes in an engaging and fast-moving manner in reacquainting us with those heroes of yesterday who've slipped into the historical shadows.

Bob Hoover is the retired book editor of the Pittsburgh Post-Gazette.

Disappointment River
By: Brian Castner.
Publisher: Doubleday, 334 pages, $28.95.
To the Edges of the Earth
By: Edward J. Larson.
Publisher: William Morrow, 352 pages, $29.99.