Monumental stony faces made horse race further (5,8)
I believe the answer is:
mount rushmore
'monumental stony faces' is the definition.
I don't know anything about this answer so I cannot tell whether it can be defined by this definition.
'horse race further' is the wordplay.
I cannot quite understand how this works, but
'horse' could be 'mount' (mount is a kind of horse) and 'mount' is located in the answer.
'race' could be 'rush' (synonyms) and 'rush' is located in the answer.
'further' could be 'more' (synonyms) and 'more' is located in the answer.
This accounts for all the letters.
This explanation may well be incorrect...
'made' acts as a link.
Can you help me to learn more?
(Other definitions for mount rushmore that I've seen before include "Where the leaders are stoned" , "national memorial" , "Where giant relief carvings of four US presidents are to be seen in South Dakota" .)