Blackthorn Peak, also known as Black Thorn, is a 4,117 foot (1,255 meter) mountain summit located at the head of Glacier Bay's Geikie Inlet in Glacier Bay National Park and Preserve, in the Fairweather Range of the Saint Elias Mountains, in southeast Alaska.

The mountain was given its descriptive name in 1896 by Harry Fielding Reid, an American geophysicist who studied glaciology in Glacier Bay.

[1] Weather permitting, Blackthorn Peak can be seen from Glacier Bay, which is a popular destination for cruise ships.

The months May through June offer the most favorable weather for viewing or climbing the peak.

[4] Weather systems coming off the Gulf of Alaska are forced upwards by the Saint Elias Mountains (orographic lift), causing heavy precipitation in the form of rainfall and snowfall.