During Curiosity's journey to Mars, it was carried by something called a cruise stage: a combination of propulsion systems, fuel tanks and other equipment required to guide the rover to its destination. On the way down, however, all that stuff made a bit of mess.
Just before the cruise stage hit Mars's atmosphere, the fuel tanks and propulsion systems were dumped — along with two 75kg blocks of tungsten ballast — to smooth the aerodynamics on the final approach. This picture shows the site at which all that extraneous baggage landed, some 80km away from Curiosity's landing site.
These pictures were captured by the Mars Reconnaissance Orbiter, and the debris has clearly left some prominent scars on the planet. It's not all bad though: because NASA had lots of information about the objects that hit the planet — how much they weighed, how fast they were moving, that kind of thing — it can analyse the images and impact dynamics to learn more about the atmosphere of Mars. Clever.