You are correct, the Austin depot was built 10 years before the 4 stall engine house. The depot was constructed 1906 and the engine house was built 1916. In 1917 a 16x42 workshop was built which I think was an addition to the engine house, but I am not certain. In 1940 a fuel oil station was built in the engine house which I presume used the west stall (one farthest from the mainline) which consisted of a steam boiler for heating the oil, a 12,000 gal storage tank and a steam pump for transfering the oil.
Operationally prior to building the engine house at Austin it must have been some exceedingly long days for crews to operate all the way to Prairie City from Baker and return. That is not to say that freights couldn't have tied up at Austin or Whitney for the night, but this is speculation. Here are a few Austin scenes from over a wide span of years. The first 3 I don't have attributed to any particular collection. #1 is dated 1906 and presumably the depot and water tank are behind the trees. #2 shows how Austin had grown by 1921. #3 is undated, but obviously prior to the engine house being constructed in 1916. The 4th photo dated 1909 came from the collection of my late friend Ron Harr, though a collectable paper dealer in LaGrande,Ore. was also selling the reprinted image, so probably not specific to Ron's collection. The final photo taken of the last regularly scheduled freight leaving Austin April 11, 1947 with Engine 251. The photo was captured by Hank Griffiths and is from the Pacific NW. NRHS collection.