The average price of a gallon of self-service regular gasoline in Riverside County dropped four-tenths of a cent Monday to $4.322, a day after rising one-tenth of a cent. The average price had dropped 12 of the past 13 days, decreasing 6 cents, according to figures from the AAA and Oil Price Information Service. It is 3.3 cents less than one week ago, 13.4 cents less than one month ago and 60.8 cents less than one year ago. It has dropped $2.051 since rising to a record $6.373 on Oct. 5, 2022.