Plain to see trail grew obscured (4,5)
I believe the answer is:
writ large
'plain to see' is the definition.
(I've seen this in another clue)
'trail grew obscured' is the wordplay.
'obscured' is an anagram indicator (I've seen 'obscure' mean this).
'trail'+'grew'='trailgrew'
'trailgrew' anagrammed gives 'WRIT LARGE'.
(Other definitions for writ large that I've seen before include "very obvious" , "on a mass scale" , "Emphasised" , "exaggerated" .)