The desert
canyon, which in spring had appeared lush with scrub oak and blooming cacti, but grew brown and sere as the hot August winds continued.
A. canyon, which in spring had appeared lush with scrub oak and blooming cacti, but grew
the desert canyon but grew .... - incorrect
B. canyon
had appeared lush with scrub oak and blooming cacti
and grew - brown and sere as the hot August winds continued. The intended meaning is changed. Both bold parts are happening at the same time - Incorrect
C. canyon which in spring had appeared lush with scrub oak and blooming cacti grows - usage of which without comma is incorrect. grows is present tense - action is going on- but the intended meaning is that the desert canyon grew brown and sere ....Incorrect
D. canyon in the spring appeared lush with scrub oak and blooming cacti, but has grown - awkward structure.
E. canyon, which in spring had appeared lush with scrub oak and blooming cacti, grew - relative clause which in spring...correctly modifies the desert canyon. the desert canyon grew brown and sere as the hot august winds continued - seems correct - as it describes how the desert canyon grew brown and sere in the past as the hot august winds continued. Correct
Answer E