It is set west of the crest of the Cascade Range, on land managed by Mount Baker-Snoqualmie National Forest.

Topographic relief is significant as the northwest aspect rises nearly 4,100 feet (1,200 meters) above the Middle Fork in 1.25 mile.

[2] Prior to 2014 when the new trail was completed, climbing Mailbox Peak involved 4,000 feet gain in only 2.6 miles along an unmaintained route that was used for conditioning for major climbs,[5] and recruits from the Fire Training Academy would celebrate graduation by carrying a fire hydrant to the summit.

Mailbox Peak is located in the marine west coast climate zone of western North America.

As a result, the west side of the Cascades experiences high precipitation, especially during the winter months in the form of snowfall.