From Nagorsen (1996:132): "Digging is most pronounced in autumn and winter when the soil is moist and easy for moles to work. This is the time of year of when Coast Moles may expand their range into new areas. It has been estimated that between October and March one Coast Mole can construct as many as 400 molehills."
Nagorsen, D.W. 1996. Opossums Shrews and Moles of British Columbia. UBC Press. 169 pp.