Boulder's smaller than this state capital, paradoxically (6,4)
I believe the answer is:
little rock
'than this state capital paradoxically' is the definition.
'Little Rock' can be an answer for 'state capital' (state capital of Arkansas). I am not certain of the rest of the definition.
'boulder's smaller' is the wordplay.
I cannot quite see how this works, but
'smaller' could be 'littler' (synonyms) and 'littler' is present in the answer.
This may be the basis of the clue (or it may be nonsense).
(Another definition for little rock that I've seen is " State capital of Arkansas".)