The topo maps at the bottom of Brian's 4x4 page seem to show the track pretty good - I spotted individual yard tracks in Cottage Grove, and a passing siding about midway up the road.
I also just picked up an old book today - copyright 1950, so it doesn't have any of the more recent history. It does have a loco roster up to that point, though, and some interesting photos (including one of the home-made combine).
The bridges were originally Howe truss, and were covered sometime after June 1909 (after rot was discovered when a train fell through the Curin bridge.) In 1948, the Wildwood bridge was replaced by a steel girder bridge. The Currin and Walden bridges were replaced next, but it doesn't give a date.
There were no turning facilities in Disston, so the engine would run backwards toward Cottage Grove with the train behind.
Roster:
1(1st) 4-4-0 Baldwin blt 1881 ex-O&SE 1 - OR&N 32 - UP 361 - OR&N 32
1 (2nd) 2-6-2T Baldwin blt 1925 ex Anderson Middleton Lumber Co. No 1. In service (as of 1950-ish)
2 2-6-0 Baldwin blt 1870 ex O&SE 2 - OR&N 15 - UP 1378 - OR&N 41 - V&T No 10
3 2-6-0 Cooke blt 1873 ex O&SE 3 SFC&W 3 - OR&N 18 - UP 1381 - OR&N 40 - V&T 16. Acquired 1906 or 1909.
4 4-4-0 Cooke blt 1886 ex O&SE 4 - C&E 4 - OP 12. Wrecked 1941.
5 4-4-0 Baldwin blt 1881 ex Mt. Hood RR 1 - OR&N 58 - UP 529 - OR&N 44. Wrecked for movie 1926.
6 2-6-0 Baldwin blt 1882 ex O&SE 6 - SP 1602 - SP 1514 - O&C 30 - OR&N 50. Acquired 1902. Sold 1916. Scrapped 1917.
7 2-6-0 Baldwin blt 1880 ex SFC&W 7 - SP 1600 - SP 1512 - O&C 20 - Western Oregon 8. Acquired 1916; sold 1927 to Walden Lumber Co as a stationary boiler.
8 4-6-0 Rhode Isl. blt 1888 ex SP 2138 - SP 1739 - SP 338. Acquired 1924; sold 1941
9 (1st) 4-4-0 Cooke blt 1886 ex C&E 9 - OP 9. Acquired 1902
9 (2nd) Shay Lima blt unknown ex A&M 9. Sold 1941
9 (3rd) 2-6-2T Richmond blt 1909 Ex National Lumber Co 26 - Winston Lumber 26. In service (as of 1950-ish)
(from Railroads Down the Valleys by Randall V. Mills. 1950.)