What is the minimum radius of curvature of cross-country railroads?

Question

I am assuming normal freight-train speeds across the country--not switching yards.

Answer 1

Very, very large: miles, I think. Trains do not turn sharp corners or steep hills, because their mass is enormous.

Answer 2

Cantara Loop, UP railroad, Black Butte-sub, 6 miles north of Dunsmuir, Ca., 15 degrees, compensated curve, 180 degree about face.  This is on the "I-5" corridor between Dunsmuir, Ca., and Klamath Falls, Oregon.  Purported to be the tightest curve on Class 1 Railroad and on my seniority district.