Travertine was used extensively by The GSSR in the construction of bridges and culverts. Most if not all of the travertine came from Los Marcelinos and was brought down to the railway by mule carts.
The company, now called 'Margar Stone' still quarries, cuts and polishes travertine from the Los Marcelinos quarry.
It is reasonable to assume that the travertine was cut at the quarry and delivered in numbered blocks for rapid assembly. Many of these blocks would have been very heavy and would have needed lifting by crane using mules or horses (of which The GSSR owned a number). Presumably, the construction engineer would only have to give the height and width of the bridge/culvert arch and the stonemasons would do the rest. Of course, this is pure conjecture.