No, this is not supported.
The spell only asks you to select (and only defines) one target location. That location must therefore contain both the raw materials and be the target for the finished product.
Nothing in the spell indicates that the location of the resources and the location of the finished product are different. My interpretation (and admittedly only that) from reading, is that you choose a location within 120 feet that has raw materials. Those raw materials assemble themselves into a finished object, but both the raw materials and the finished object are bounded by the same volume constraint (a 5' cube for minerals and metal, 8 contiguous 5'cubes for everything else) and occupy the same location. I.e., the start and finish locations are one in the same.
So, material will move freely within the volume allotted based on the material, but you do not get to use the spell to excavate one area AND create an object in a completely different one, unless you can connect those two locations within the same bounding volume as specified by the spell.
This does allow a poor man's meteor strike to occur by dropping 5 square feet of non-mineral material from about 35' above and 5' over from its starting position by choosing a 5' cube of stuff, and chaining your 8 5' cubes to go up 35', then over 5', then your finished object is left suspended in air, whereupon gravity takes over. I wouldn't allow this, and insist on the final product requiring a solid surface to be fabricated on, but that is simply a personal interpretation and not strictly supported by the text.
And yes, by this interpretation, your bridge would be constructed on land and need to be moved into its final position manually (unless the trees were suitably close to the water). Considering the space constraints of the spell, it is a fairly small bridge anyway, so this is not unreasonable.