The oil-rich city of Carson has imposed an emergency moratorium on all new drilling, halting efforts by a petroleum company to bore more than 200 wells near homes and a state university. The drilling ban, which runs for 45 days but could be extended up to two years, was driven by a fear that Occidental Petroleum would employ hydraulic fracturing to coax oil from one of the city's vast oil fields. Occidental has repeatedly denied it will use fracking, an extraction technique that involves blasting a mix of water, chemicals and sand deep into the ground to fracture rock formations and free trapped oil. Critics contend the practice can contaminate groundwater or even trigger earthquakes when water is injected underground. "There are too many questions, too many unknowns," said Councilman Al Robles, who proposed the moratorium. "I refuse to gamble with the health and well-being of the residents."