Having toured a few US Navy ships, Amtrak is nothing like those. I remember seeing some personnel demonstrate how to shoot right down by hanging by the railings and not touching the stairs. Navy stairs are more like ladders.
Superliner stairwells are somewhat narrow, with stainless steel handrails and a "dobby" nonslip rubberized surface. The stairs are at about a 45° angle. I found a photo. They're not particularly challenging, but they're not super easy either. I found this photo, which should give a pretty good idea.
California cars are a bit different, but about the same difficulty.