  We report on mapping of the north polar region of Mars using data from the
Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) instrument. We
have observed three Mars Years (28-30) of late-winter and spring recessions
(Ls=304{\deg}-92{\deg}). Our investigations have led to the following
observations: 1. We classify the retreat of the north polar seasonal cap into
'pre-sublimation', 'early spring', 'asymmetric' and 'stable' periods according
to the prevalent H2O ice grain size distributions. 2. During the early spring,
the signatures of CO2 ice at the edge of the cap are obscured by H2O ice, which
increases the apparent size of the H2O ice annulus around the seasonal CO2 cap
at this time. At around Ls=25{\deg}, this process changes into an asymmetrical
distribution of H2O deposition, covering CO2 signatures more rapidly in the
longitude range from 90-210{\deg}E. 3. We detect signatures of 'pure' CO2 ice
in extremely limited locations (in Lomonosov Crater) even in mid winter. H2O
ice signatures appear everywhere in the retreating CO2 seasonal cap, in
contrast with the south polar seasonal cap. 4. We find that average H2O ice
grain sizes continuously increase from northern mid-winter to the end of
springtime - this is the inverse of the behavior of CO2 ice grain sizes in the
southern springtime.
