Galloping Gertie (properly known as the Tocama Narrows Bridge) opened on 1st June 1940. It collapsed into Puget Sound on 6th November 1940. The collapse was caused by aeroelastic flutter. To see what that means in practice take a gander at this video:
Since the failure took some time no people were injured. Here is the account of Leonard Coatsworth the owner of the car that went down with the bridge.
Just as I drove past the towers, the bridge began to sway violently from side to side. Before I realized it, the tilt became so violent that I lost control of the car…I jammed on the brakes and got out, only to be thrown onto my face against the curb…Around me I could hear concrete cracking…The car itself began to slide from side to side of the roadway.
On hands and knees most of the time, I crawled 500 yards [450 m] or more to the towers…My breath was coming in gasps; my knees were raw and bleeding, my hands bruised and swollen from gripping the concrete curb…Toward the last, I risked rising to my feet and running a few yards at a time…Safely back at the toll plaza, I saw the bridge in its final collapse and saw my car plunge into the Narrows.
Coatsworth’s cocker spaniel Tubby was lost with the car.