The original transcontinental railroad, the combined Union Pacific and Central Pacific lines, opened in 1869. The route was far from straight, as it curved around various mountains and ridges, following shallow grades as much as was possible while crossing the Rockies and Sierra Nevada. It also curved around the Great Salt Lake in Utah, and that curve included some substantial changes in grade. There was an obvious, if extreme, solution to the problem caused by the lake: run the trains over the lake, eliminating the big northward arc of the route and eliminating the changes in grade along that arc. That obvious solution just required running railroad track over some 20 miles of open water.
The result, constructed 1902 to 1904 can be seen above. More than half of the over-lake track was laid on a wooden trestle constructed on timber piles driven in the lake-bottom mud; the remainder was several earth-fill causeways. Technically a trestle is a bridge, but it doesn’t really feel like one: the spans between the timbers are quite short, and the overall structure is so long that it can’t be taken in all at once from any angle. Here’s a map from the HAER survey:
Note that the original route was, in part, on the Promontory peninsula at the north end of the over-lake route. Timber trestles are problematic anywhere, as the timber, no matter how it is treated, is still subject to rot, insect attack, and fire. Eventually, the successor railroad decided to replace the trestle portion of the route with an earth causeway to match the causeway sections already in use. The causeway was built in the 1950s; removal of the trestle began in the 1970s, shortly after the HAER report was created.
A phrase that engineers typically first hear when they are students is “an elegant solution.” There’s no single clear definition of what that means, because it is context dependent. It is quite possible that the designers of the trestle around 1900 thought they had an elegant solution to the railroad’s problems, cutting across the lake to shorten and flatten the route. It is quite possible that the designers of the replacement causeway thought they had an elegant solution to the difficulties of maintaining the trestle. From my easy perch, decades later and without having to face the reality of running a rail line through difficult terrain, this looks like the opposite of elegance.