Near dodge city there is a giant concrete cross- a monument to the first catholic mass performed in the new world. Inside that cross the party fount a box, and inside that box they found another cross- this one golden and bejeweled. They also found a scrap of parchment.
The cross was saturated in strange magics attempts to perceive and identify those magics brought the songs of angels and the stench of bodies rotting to the minds of the characters. When Alex took the cross into the Umbra he was swarmed by the sorts of scavenger insects who feed upon corpses.
The site of the concrete cross was not magical in any way, instead it was distinctly non-magical. It was extremely uninteresting in all ways, almost no one they talked to could tell them anything about it or had any interest in it what so ever. The entire effect was something like the Arcane cloaking that Veronica uses to divert both mundane and magical attention.
One little old woman remembered the creation of the cross quite well, however, and she told them quite a bit about the handsome foreign priest who came from Spain to build it.
When the cross was stolen from the party by Miles it was used by the party’s enemies to gain access to the city of gold, where wishes come true. This altered reality quite a bit.