CREATE TABLE table_63523 ("Club" TEXT, "League" TEXT, "Sport" TEXT, "Venue" TEXT, "Established" FLOAT, "Capacity" FLOAT)

What is the league established before 1930 with the rayo vallecano club?
SELECT "League" FROM table_63523 WHERE "Established" < '1930' AND "Club" = 'rayo vallecano'
SELECT "League" FROM "table_63523" WHERE "Club" = 'rayo vallecano' AND "Established" < '1930'