A 90-day countdown began Monday for to force the effective legalization of simple possession of marijuana in B.C.

Volunteers for Sensible B.C., led by long-time drug legalization advocate Dana Larsen, have until Dec. 5 to collect more than 400,000 signatures. Using the same law that forced repeal of the harmonized sales tax, the petition to trigger a province-wide referendum needs support from 10 per cent of registered voters in each of B.C.'s 85 electoral districts.

Larsen has proposed that B.C. go around the federal prohibition with a "" that would disallow the use of B.C. police resources to prosecute simple possession of small amounts of pot by adults.

Marijuana possession cases still account for 60 per cent of drug violation reports to police in B.C., according to Statistics Canada figures from 2012. But the number of cases declined 10 per cent from 2011.

There were 25,432 police-reported incidents of all types of drug offences in B.C. last year, a 7.4 per cent decline from 2011. Marijuana trafficking cases declined more than 20 per cent to 1,006 incidents, and importation and exportation of marijuana declined by 40 per cent.

Marijuana growing cases declined 4.6 per cent, following a 28.6 per cent drop in 2011.

The petition follows a proposal by police chiefs across Canada to make simple possession of marijuana a ticket offence, to keep minor cases out of court. Prime Minister Stephen Harper said his government would consider the change, but it remains opposed to any decriminalization or legalization.