Shasta knotweed (Polygonum shastense), closeup showing the distinctive leaves, folded in half when emerging and later with two very distinct folds or veins on the top side.  At 10,380ft along trail between Saddlebag and Steelhead Lakes in 20-Lakes Basin, Hoover Wilderness, Sierra Nevada mountains, California USA.
<a href="//commons.wikimedia.org/wiki/User:Dcrjsr" title="User:Dcrjsr">Dcrjsr</a>
CC BY 3.0
<span class="int-own-work" lang="en">Own work</span>