Cowardly notes about national park (11)
I believe the answer is:
yellowstone
'national park' is the definition.
(I've seen this before)
'cowardly notes about' is the wordplay.
'cowardly' becomes 'yellow' (yellow can informally mean cowardly).
'about' indicates an anagram.
'notes' anagrammed gives 'stone'.
'yellow'+'stone'='YELLOWSTONE'
(Other definitions for yellowstone that I've seen before include "Topaz, perhaps" , "River with falls in Wyoming" , "US river" , "First US national park, 1872" .)