I've tried the other "how to clip" instructions here, but consistently get an empty shapefile from the clip.
QGIS Version: 2.4.0-Chugiak
OS: MacOS 10.10
Input File: San Diego (South Map) 1999 Topo (2' intervals) (1 GB Download Link)
I've assigned the same CRS from the San Diego Vector Layer to the polygon clipping mask.
Here is a screen capture of my process:
Hopefully someone can point out where I'm going wrong with this process.