I'll add a couple more to the list:
The last time I was in Wisconsin Rapids, the GB&W had a roundhouse but no turntable. Don't know if it is still there. C&NW and MILW had enginehouses there, too, but I don't remember if they were roundhouses.
UP's ex-D&RGW Burnham shops in Denver had a turntable, but no roundhouse the last time I looked on Google Earth. The roundhouse has been replaced by a linear shop, but a couple tracks extend out the back of the building to the turntable. If you look on Google Earth, you can still see the "ghost" of the little narrow gauge turntable. Like many features that show up on satellite pictures, I'm not sure if this can be seen from ground level.
When I worked for the Rock Island at Iowa Falls, our yard office was located in the surviving office annex of the 1869 roundhouse. Several stalls remained, but no turntable or rail access to the building. The stalls were used as storage space for a local grain elevator.
There are still lots of remnants of roundhouses no longer in service. The foundations, including filled-in inspection pits, of the AT&SF roundhouse at Deming, NM are still there. The turntable pit for the C&NW at Pierre, SD exists as a place trucks can back up to loading dock doors. The roundhouse for the CB&Q exists without rail connection at Deadwood, SD. This building has an extended stall for parking mallets. The old Midland Terminal roundhouse at Colorado Springs is a pottery works. The C&NW roundhouse and turntable at Rapid City were still in use when I worked for the DM&E. There must be many more, especially in railroad-rich places like Chicago.
Les
