Like say, if gold is discovered in Alaska?
I think so. Wasn't gold discovered in 1848 or thereabouts? I think if the rush becomes bigger then it may speed up the RR's development by I at least a few years.
There were rumors in 1848 (around the same time gold was discovered in California) but I don't think substantive discoveries were made until the 1860s or 1870s.
Probably not hard to develop a realistic POD where substantive discoveries of gold are made in Alaska in the 1840s.
The big gold rush in the Yukon wasnt until 1896.