Defending champion Spanish Fern and Tranquility Lake head a field of six entered in Saturday's $500,000 Yellow Ribbon Stakes (gr. IT) at Santa Anita's Oak Tree meeting. Earlier in the day, undefeated Flame Thrower heads a field of eight entered in the $200,000 Norfolk Stakes (gr. II).Spanish Fern, who will be ridden by Victor Espinoza in the 1 1/4-mile race for fillies and mares, has won just one of eight starts since last year's Yellow Ribbon. Overall, Spanish Fern has won six of 18 starts and earned $648,368.Tranquility Lake, who faded to finish last in the Yellow Ribbon last year, has won her last two starts and seven of 17 overall races with earnings of $693,660. Tranquility Lake will be ridden by Eddie Delahoussaye.Caffe Latte, to be ridden by Brice Blanc, also figures as a contender, having won five of 12 starts with earnings of $666,868. In her last race, she won the Ramona Handicap (gr. IT) by 1 1/4 lengths over Tout Charmant.Flame Thrower has won all three of his lifetime starts and earned $268,200. He will be ridden for the first time by Espinoza in the one-mile race for 2-year-olds because Corey Nakatani, the colt's regular jockey, is sidelined due to a broken collarbone.The $300,000 Clement L. Hirsch Memorial Turf Championship (gr. IT) and $200,000 Oak Leaf Stakes (gr. I) will be contested Sunday. A field of six headed by Mash One, who hasn't raced since winning what was known as the Oak Tree Turf Championship last Oct. 3, is entered in the Hirsch, a 1 1/4-mile event for 3-year-olds and up. The name of the race was changed this year in memory of Hirsch, a former Oak Tree president, owner, and breeder who died last March. Mash One, a 6-year-old Chilean-bred who has won six of 16 starts and earned $369,583, has been bothered hoof ailments.Also entered is Argentine import Asidero, who has won five straight Group I events in his native country and seven of 10 starts overall with earnings of $565,791. Cindy's Hero and Notable Career head a field of seven entered in the Oak Leaf Stakes, a one-mile race for 2-year-old fillies.