The clone command allows blocks to be copied to other locations that are loaded in memory.

/clone x1 y1 z1 x2 y2 z2 [clonemode] [taskset]

Where x1 y1 z1 and x2 y2 z2 are the opposing corners of the bounding box that you are cloning, and and will be the north western corner of the cloned blocks.
In order to make this command work, both the source blocks and destination blocks must be loaded. It is much easier to do with 2 people if you are moving or copying areas over large distances.