Who were the winning riders of the championship in Euer Valley, CA and whose horse was Magic Sirocco?
CREATE TABLE "world_championship_winners" (
  "year" real,
  "location" text,
  "distance_miles" real,
  "rider_names" text,
  "horse_name" text,
  "best_conditioned_horse" text
);
SELECT "rider_names" FROM "world_championship_winners" WHERE "location"='Euer Valley, CA' AND "horse_name"='Magic Sirocco';