Re: rail size, South Park ca 1935, RGS 1944, D&RGW 1947

All of this is "Main Track", lighter rail on some sidings, spurs and in yards is almost certain. Lots of it on RGS.

On page 17 of the C&S Leadville Line Study, reprinted by CRRM, the following information is presented:
85 lb 0.07 miles
80 lb 4.12 mi
60 lb 12.65 mi
56 lb 22.65 mi
52 lb 86.80 mi
50 lb 14.42 mi
45 lb 16.09 mi
40 lb 6.59 mi

RGS, from Sunset on the RGS Vol. II, pg 117

60 lb 26.40 mi (mostly north of Vance Jct, Keystone hill)
57 lb 33.83 mi (mostly Vance Jct-Rico)
56 lb 5.12 mi (Dallas Divide)
52 lb 46.31 mi (mostly Mancos-Denby, Telluride br)
45 lb 6.00 mi (Denby - Porter)
40 lb 54.50 mi (mostly Rico-Durango)

D&RGW, from profiles in Mudhens, pgs 148-154 [any addition errors mine]

90 lb 39.28 mi (Marshall Pass, 3-rail north of Antonito, CB, Monarch & Silverton brs)
85 lb 87.26 mi (Marshall Pass, Cumbres, Poncha Pass, CB, Monarch & Silverton brs)
75 lb 34.12 mi (all on Farmington branch)
70 lb 172.06 mi (Marshall, Cumbres, Chama-Durango, Baldwin br)
65 lb 134.09 mi (everywhere except Alamosa-Carbon Jct, Baldwin br)
60 lb 5.88 mi (Black Canyon, Valley Line)
57 lb 3.35 mi (Valley Line)
52 lb 24.13 mi (Silverton Br, Valley Line)
45 lb 30.00 mi (Valley Line, Ridgway-Ouray)
40 lb 1.42 mi (Ouray)
35 lb 0.38 mi (Baldwin br)
30 lb 0.39 mi (Anthracite, Ouray)

Whew!
Hank