Well, crop circles are carried out by a somewhat secretive network of artists, farmers, and such. They get a pilot to do a fly-over of the area to get photos for mapping it out, mark the spots, then are able to do an entire field in just one night. I suppose nowadays they use GPS to make it even easier, you don't need folks planting little stakes in the ground beforehand.
As for the Nazca lines, that is literally just trenches dug out of the iron oxide rock making up the desert's floor around there. They are basically all but confirmed to be religious sites used for sacrifices and offerings, as various alters shells bones and pots are found all around there. I'd be willing to bet they were created with a crude form of a camera obscura using the reflection to plan out the shapes.