Stagg, Giant sequoia in Alder Creek Grove, Giant Sequoia National Monument, US

Stagg, officially the Amos Alonzo Stagg Tree and formerly the Day Tree, is a giant sequoia in Alder Creek Grove in the Sierra Nevada. It is the fifth largest tree in the world and the tallest giant sequoia south of the Lincoln Tree. Its trunk measures 109 ft (33 m) in circumference at ground level, the second largest footprint of any living giant sequoia after the Boole Tree.

This tree has survived for thousands of years and witnessed countless environmental changes and wildfires that shaped its growth rings. The monument was established to protect these ancient trees and ensure their preservation for future generations.

The tree's name honours Amos Alonzo Stagg (1862–1965), the University of Chicago football coach who spent much of his later life coaching in Stockton, in the San Joaquin Valley below the grove; it was renamed for him in 1960, having previously been called the Day Tree. L. Day first noticed the tree in 1931 and measured it in 1932 with two helpers.

Stagg stands on private land of the Rouch family in Alder Creek Grove but is freely open to the public. Access is by foot through the grove; the tree is the tallest giant sequoia south of the Lincoln Tree in Sequoia National Park. In 2020 firefighters set a sprinkler system around it to keep the Castle Fire away.

In 1993 a group of climbers scaled the full height of Stagg and found a hollow room inside the trunk near the very top, a cavity most visitors never suspect from the ground.