editing the archive? template

Hi all

Tried to search but can't find the answer.

I've created a post type - Vendors. I've created a taxonomy - Vendor_Type, non-hierarchical.

With the vendors I've created I've added three taxonomies, Type1, Type 2, Type 3.

I used a plugin - custom taxonomies menu widget - to list the taxonomies in the sidebar.

When I click on one of the taxonomies in the sidebar, I am given a page that appears to be an archive page - http://mysite.com/vendor_type/Type1/ - Where is the layout for this page coming from? What template is used to produce this page?

Thanks
Lori

edited to add that I don't think the sidebar widget has anything to do with the template