Bill Wolfenbarger can clarify ... as I recall there was quite a bit of KOL-AM/FM overlap in mid-70's (KOL became KMPS in Sept, 1975). That was probably first stab at Top 40 in the market. KNBQ (now KIRO-FM) was doing an automated version of Top 40 with Drake-Chenault supplied reel tapes around the same time frame. In 1976, "the fm kvi" went on air @ 101.5 (now KPLZ), leaning slightly more Adult than pure Top 40. KYYX did full-on Top 40, but with automated toys and jocks tracked their dropins. KNBQ went "live" around 1978/early 1979, about the same time fm/KVI became K-PLUS (with calls change to KPLZ). Then, KYYX went to "rock of 80's"/"wave" format, abandoning the Top 40 ... and by then AM was dying as go-to-destination for music. KUBE launched, taking over old KBLE-FM frequency ... became the real powerhouse in town (mostly with support from veteran morning man Charlie Brown)....KHIT launched @ 106.9 using a Bremerton station relocated to Seattle .... but didn't last too long (became "new age"). KUBE-KPLZ-KNBQ battled for a bit, with KNBQ dropping out to take on oldies as KBSG. KUBE-KPLZ continued into the 1990s, when the music product basically killed the dominance (HipHop, fragmented pop, etc.). KUBE eventually chose the Rhythmic path, KPLZ tried to stay mainstream; but by 1994 decided to refocus as adult CHR, then gold-based AC (launching the "Star 101.5" moniker), then back to currents-based Adult format that it does now.
The ironic thing behind all this, is that KOL was probably a little too early to try to be FM leader and was focused on holding the "album" brand on their FM as long as they could. KJR bought KISW, and launched it right away as active rock station. They wound up competing head-to-head for years with KZOK. KING's FM was locked in to classical because of the woman who owned the company adored the format. All this took place years ahead of station limits .... otherwise, highly likely KJR and KING would have launched an FM counterpart and shifted their product to FM as the audience was shifting; but their format choices on their FM's were already locked in to other choices. So all the AM Top-40 heritage stations died when AM music died (including KTAC in Tacoma, whose FM was dedicated to "Beautiful Music"). When KOL was sold, their FM was dedicated to Beautiful music as well (which was the #1 billing format in the market in the mid-70's ... what is now the WOLF @ 100.7 was KIRO's FM entry into Beautiful Music as KSEA and owned the ratings). Eventually, KMPS (former KOL) decided there was huge opportunity to launch their country product on FM, so 94.1 because KMPS (FM)...and it wound up completely killing the legendary KAYO (1150).