Petunia Peak is a 6,953-foot (2,119-metre) mountain summit located in Jefferson County of Washington state.

Precipitation runoff from Petunia Peak drains into tributaries of the Dungeness River, and topographic relief is significant as the east aspect rises 3,750 feet (1,143 m) above the river in approximately 1.7 mile, and the west aspect rises 2,000 feet above Royal Basin in less than one mile.

Like the town of Sequim 17 miles to the north, Petunia Peak lies in the rain shadow of the Olympic Mountains.

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

As fronts approach, they are forced upward by the peaks (orographic lift), causing them to drop their moisture in the form of rain or snow.