"Frontier Rail" is a collection of companies under common control and ownership. I'm not sure which railroad or company "owns" the individual locomotives - the reporting marks (LRY, YCR, CCET) in use happen to be their common carrier operations that have assigned reporting marks that are being used for convenience of movement and may not indicate assignment or ownership. The common name of an operation may not match the LLC name.

According to their website - the Tri-Cities switching operation is the Kennewick Terminal. http://frontierrail.com/map/

SP abandoned the Lakeview branch in the 1980s, the county bought it to save their rail connection. The first contract operator backed out at the last minute, so Great Western operate for many years as their NCO Division. They used at least two former BN GP9s, maybe one or two more rotated through. I do remember one being a chop nose with dual controls stands and 6BL brakes, the other was high nose. The county operated its Lake County Railroad itself after Great Western. IIRC they bought one of the GWRR GP9s. I remember stopping by Lakeview enginehouse one day and finding a pile of parts suggesting a conversion to 26L brakes. I believe the former SD&AE/KYLE "Blue Goose" GP9 M-K rebuild was there just a short time, and may have been leased or traded to Western Rail. It went back to them and I was told was sold to an industrial customer - so it is still out there somewhere. (Does SJVR still have one in operation?). This was replaced by the 700, another M-K rebuild. When Modoc Northern took over the Lake County RR they repainted the 700 as theirs (though apparently it was still owned by Lake County), had a cylinder disintegrate and then let it freeze.

When Frontier got the contract to operate the Lake County, the original power was an xATSF B23-7 leased from NRE by the perlite shipper. This was replace by a GP49. The 700 was repaired (now owned by Frontier?). I have heard that a couple engines might be out of service at the moment pending repair.

Frontier has assembled a substantial fleet of locomotives (most owned?) for their growing list of operations. Just of the top of my head and of questionable accuracy:

The 5 SD45s mentioned elsewhere in this thread.
5 GP49s (2 Lakeview, others in Ohio - 1 CCET, 1 leased out?)
1 SW1000 (Portland)
1 B23-7 (Portland)
1 SW9R (WWR - Frontier is a partner in WWR)
1 xUP/CP SW10 (Delano)
1 xCBR SW1200 (on WWR for repair)
3? RS4TC (YCR + 2 LRY)
2-3 xUP MP15DC (Wallula, Boardman oos, and ??)
2 xNS GP38-2 (Lakeview? maybe other replacing GP9 lease unit in New York?)

Engines may maintain an assignment for years, or move several times in a few years.