Historical Aerial Photo Images

I'm working with a local North Carolina land conservancy on a new preserve and have just started working with CalTOPO for trail planning, mapping and parcel history. So far, I'm having a lot of fun with it.  However, the only air photo image I see in CalTOPO is a summer, leaves out, image, with no date given.  I'm kind of surprised since winter images can provide so much information for trail planning and dates would seem to be critical (Is the image out-of-date?). I'm curious if CalTOPO has other air photo image files available.

Luckily, our local county GIS System has a good series of historical images, most of which are winter images. I understand that I can download these as Mapsheets, especially if I can get georeferenced PDF images, which I'm working on getting from the county.

Thanks,

--Steve Gartrell