Employment in Kern County oil fields shrank by 1,200 jobs in January and February, or 10 percent, according to state data released Friday. The layoffs, a result of plummeting oil prices, made up about one-eighth of Kern's 9,900-job reduction across all industries during the first two months of this year, when the county's jobless rate jumped one full point to an estimated 11 percent in February, the data from California's Employment Development Department show.