  As a part of the Milky Way Imaging Scroll Painting (MWISP) survey, we
performed a simultaneous 12CO(1-0), 13CO(1-0), C18O(1-0) mapping toward
molecular clouds in a region encompassing 3.75 square degrees. We reveal three
molecular clouds, the 15 km/s cloud, the 27 km/s cloud, and the 50 km/s cloud,
in the surveyed region. The 50 km/s cloud is resolved with an angular
resolution of around 1' for the first time. Investigating their morphology and
velocity structures, we find that the 27 km/s cloud is likely affected by
feedback from the stellar association Mon OB3 and the 50 km/s cloud is
characterised by three large expanding molecular shells. The region is mapped
in C18O (1-0) for the first time. We discover seven C18O clumps, which are
likely to form massive stars, and 15 dust clumps based on the BGPS archival
data. Using infrared color-color diagrams, we find 56 Class I and 107 Class II
young stellar object (YSO) candidates. According to the distribution of YSO
candidates, an overdensity is found around the HII region S287 and the
intersection of two shells, indicative of triggering. The star formation
efficiency and rate of the 27~km/s cloud are discussed. Comparing the observed
values of the filament S287-main with the models of fragmentation, we suggest
that turbulence controls the large scale of fragmentation in the filament while
gravitational fragmentation plays an important role in the formation of YSOs on
the small scale. We find that star-forming gas tends to have higher excitation
temperature, higher 13CO opacity, and higher column density than
non-star-forming gas, which is consistent with the point that star formation
happens in denser gas and star-forming gas is heated by YSOs. Using the 1.1 mm
dust emission to trace dense gas, we obtain a dense gas fraction of 2.7%-10.4%
for the 27 km/s cloud.
