Gives an impression of American mounting horse on street in the centre of Fresno (8)
I believe the answer is:
suggests
'gives an impression of' is the definition.
'american mounting horse on street in the centre of fresno' is the subsidiary indication.
'american mounting' becomes 'su' (I can't justify this - if you can you should believe this answer much more).
'horse' becomes 'gg'.
'on street' becomes 'st' (I've seen this in other clues).
'in the' is an insertion indicator.
'centre of' says to take the centre.
The middle letters of 'fresno' are 'es'.
'st' inserted inside 'es' is 'ests'.
'su'+'gg'+'ests'='suggests'
(Other definitions for suggests that I've seen before include "Puts forward for consideration" , "Puts forward for discussion" , "counsels" , "Proposes" , "Makes a proposal" .)