I have a map layer showing all the rock types in Pennsylvania. I need to create a new layer focusing on a smaller area of the map (to export). When I try to select the rectangular area I want, the attributes selected extend passed this defined area, but I need them to stop in the defined area, so I have a nice clean rectangle in the end. I do not have a spatial analyst license.
You could create a rectangle feature class and use the clip tool to extract the rock type layer to the exact extent of the rectangle area you want.
The link below explains how to export a layer or a selected part of a layer
One possible work around is to create a new polygon shapefile for your area of interest to use as "Mask" and then clip your rock types data layer to give it the rectangular shape you need.
You can do this by bringing your rock types and the "Mask" polygon into an mxd. and then clicking the Geoprocessing tab at top of your map document and choose the Clip geoprocessing tool.
Also, here's a YouTube video showing to how to use the tool. How to Clip a Data Layer in ArcMap 10 - YouTube
Hope this helps!