'Fraid not. This used to happen a while back; either pages for both British English and American English would exist, or more often editors would fight to move a page from one to the other. In June 2005, the Wikipedia:Arbitration Committee ruled that "when either of two styles is acceptable, it is inappropriate for a Wikipedia editor to change from one style to another unless there is some substantial reason for the change. For example, with respect to British spelling as opposed to American spelling, it would only be acceptable to change from American spelling to British spelling if the article concerned a British topic." So since an enterprising Brit got there first, American English words like millimeter and liter redirect to the British English equivalent, but the opposite is true for colour or carburettor.

In the case of geologic map, an American was the first to create the article, so you have to edit that page. However, here's a few suggestions of what you can do:
The text in bold in the opening line should reflect the title of the article. Therefore, since geological map redirects to the page, you can change the first sentence to read "A geologic map or geological map is a special-purpose map made to show subsurface geological features."
If there's a difference between U.S. and U.K. maps, I'd split the two into separate sections after the opening paragraph, and detail the differences for each (re-ordering the page as I'd done with this edit). If there's no difference, I'd just remove the specific references to the United States as being unnecessary, and expand on what's there.
You can also provide links to British geological maps if such a resource exists, as has already been done for USGS maps.

An explanation of the style ruling can be found at Wikipedia:Manual of Style#Disputes over style issues and Wikipedia:Manual of Style#National varieties of English, or if you're really bored you can read the original case at Wikipedia:Requests for arbitration/Jguk, which concerned and edit war over the use of BC or BCE for Biblical dates. Hope all this helps!