SR Bicycles of San Diego was an importer of Japanese bicycles into the San Diego area in the late 70's to early 80's. It was not related to the Japanese bicycle component company SR (Sakae Ringyo)1).
SR Bicycles knowingly were capitalizing on Sakae Ringyo's good brand reputation as their ad to the right reads: “SR uses SR, Shimano and Suntour components to give you that same kind of solid value for your dollar that the four-wheel Japanese imports have shown.” SR Bicycles imported quality Japanese frames with the best on and off road Japanese components.
SR Bicycles only briefly imported mountain bikes for the years 1983 → 1985.
San Diego Reader, August 9, 1984. sandiegoreader
Pics are of a rebuilt bike. Originally it was spec'd with SunTour GT Cyclone (1981-5) and SunTour power shifters (1983-5). As shown, it has a 1986 Light Action rear derailleur.
1983 Explorer reddit
Odd mix of Shimano/SunTour - perhaps non-original? 1984 Explorers came with MounTech rear derailleurs. TIG welded. SunTour Mountech front, Deore XT rear (1983-4), SunTour LD-2800 Power Shifters (1983-5). The frame differs from the 1983 in that it now has double top tube cable guides, a unicrown fork crown, and more bottle cage mounts. And an “Explorer” decal, which doesn't exist on earlier examples.
Shimano XT, Salsa Stem, SunTour RollerCam brakes
1984 Explorer mtbr
1985 Sierra Sport
Identical frame to the 1983 Explorer, except with new decals. It's likely later than a 1984, as the SS isn't listed in their 1984 adverts. Suntour Cyclone M2 GT rear derailleur (1981-5).
It's quite possible the dates are wrong in all of these pics. There are a few other online examples, which all match the above bikes.
1985 Sierra Sport craigslist