The CP's engines ranged in weight from 56,000 to 77,450 at the heaviest and they would average out at about 62-65,000 lbs.
I can imagine that the Union Pacific's requirement was about the same so — for the total mileage of the transcontinental railroad of 1776 miles required 177,600 tons (metric tons) of rail for the track alone. more that a standard 2000 lb ton andthat if you reported the railtonnageat a 2,000 lb./ton the total rail weight alone would weigh198,912 tons of iron rail. Just remember that in the 1860's that rail was measured by the metric ton but bolts, spikes and rail fastenings were measured by the standard 2,000 lb. Then you would have to add the weight of spikes bolts, rail chairs, fish plates (rail fastenings).
One hundred tons per mile included the main line and all the side track, incidental uses and waste.
Using that method of measurement the Central Pacific railroads 690 miles of track would have been approximately 69,000 (metric tons 2240#) tons of rail.
About 200,000 net tons of iron total were used just for building the railroad from Omaha to Sacramento [at 2000 lbs/net ton, the modern useage, also called the short ton; the metric ton = 1000 kg ].
Details, at 60 lb/yard (per single rail) single track from Omaha to Sacramento: 1776 miles x 60 lb/yard x 5280 feet/mile x 1/3 yards/feet x 2 rails x 1/2000 ton/lb = (1776*60*5280*2)/(3*2000) = 187,546 tons of iron.