Here is a extremely easy way to take away the bsp from a map.
Tools needed:
Hex editor
Bloodgulch.map
Basic knowledge of hex editing
In a halo full version header, it tells you where certain things are within the map. It states that the bsp of a map begins at the offset of 0x00000800. The bsp size then continues for 0x00172800 ending at 0x00173600.
What we are going to do today is null out the bsp for the bloodgulch ground area. Nothing else (like the scenery, or weapons, etc.)
First off open up your hex editor (if you dont already have one try hex workshop)
Then goto the offset of 0x00000910
You will see '7F15' change that to '0000'
Click 'Save'/'Save As'

Then you will see a nulled out bsp game like so:
