This is a Genuine Railroad Spike, collected along the tracks of the Denver and Rio Grande Railroad.
The Railroad Spike anchors the Track to the Railroad Ties, which are wooden beams laid perpendicular to the track as the foundation. There are approximately 3,520 ties per mile of track. Each tie required a minimum of 4 spikes, so as you can imagine, they went through a lot of spikes. This amazing piece of history makes a great gift or conversation starter!