David: 1981 was an interesting moment in K-EARTH history. Bob Hamilton took over as PD in the first quarter of 1977 and took it from oldies to what RKO called "Adult Contemporary" but what R&R rightly saw as another Top 40 station---and listed it as such over RKO's protests. While KTNQ siphoned off pre-teens, KMET teens and KFI what few adults KHJ had left by that point, KRTH took younger women by playing 90% of KHJ's playlist in stereo with less talk and fewer commercials.
By 1981, with KHJ having flipped to Country, K-EARTH was RKO's L.A. winner and Hamilton, rather than playing it safe, decided to stretch a little---or a lot, really. And part of his strategy was a deliberate, overt appeal to the Hispanic citizens of Los Angeles. Summer of '81 saw billboards up in heavily hispanic neighborhoods---orange with the K-EARTH globe logo in the center and the words "Jugando sus favorotos. K-EARTH 101".
I don't have 1980 numbers, but KRTH was #8 in the fall '79 Arbitron book, #11 in the fall '81 and wouldn't see the Top 10 again until Bill Drake, Robert W. Morgan and the Real Don Steele arrived in the early 90s. Hamilton was gone by '86 and the station went oldies again.