60ft deep in Winter, and possibly even in Summer on some lakes, is not out of the realm of possiblity. But, it would have to be a lake that was well oxygenated at that depth. If the fish are at 60ft - they're there for a reason ... :D
The "bite" may be subtle, and therefore hard to detect ... but, a "watcher" (line watcher or rod tip watcher) should be able to see that telltale sign that something "extracurricular" is going on down there ...LOL!!
ID'ing ANY fish species on sonar is tough, unless you're catching some of them ...LOL!! Supposedly, Crappie tend to school in a "pancake" formation (when they are schooled and suspended in the water column) ... so I wouldn't think a "vertical" stack of "fish symbols" would be a good indication of a school of Crappie. Most of the time, when I see a vertical stacking of fish symbols on a depthfinder, it's White Bass or Hybrid Stripers (and the occasional pod of Largemouth). Maybe, with a high end depthfinder, one may be able to discern a species by the shape or formation of the school ... but, where they are located / depth / area structure / presence of baitfish / cover in close proximity/ and other factors may be a better indication of what fish is actually showing up on the screen. Even if all indications point to the 'signals' being a school of Crappie ... there could very well be other species of fish in that same area - and they might be in more of a biting mood than the Crappie ...LOL!! Best advice I can give is to put your bait down there and see what bites ! ...............cp