How can I create a polygon of a specific dimension?

[KeithAdams1]

I am trying to create a firebreak along a ridge line that follows a boundary file I have. I'd like the polygon to follow the length of the boundary while remaining 20 ft wide for the entire length of the polygon. 

Does anyone know how to accomplish this? 

[DavidPike · Accepted solution]

Hi, you could make a copy of the boundary file and use the 'cut' tool on the editor toolbar to only get the boundary you want. If this line is made up of lots of features you may have to select them all then 'merge' on the same toolbar. After this, select your boundary line and search for 'buffer' the documentation of this tool explains it far better than I could. To adjust the ends of your resultant feature, you may wish to use the editing toolbar to shape them as required.

[KeithAdams1]

That was exactly what I needed! Thanks much David! 

[DanPatterson_Retired]

Since you already have a polyline, you can perform one-sided buffering if you have an Advanced license.

If you have it, you simply need to specify the side of the polyline to buffer and the end type required.

Buffer—Help | Documentation 

It would make it simpler if you dissolved/unioned the entire polyline to be one feature so you only have to deal with 2 ends.

Barring the required license, you are stuck with a standard buffer and splitting it with an extended version of your ridge line as suggested