Here's a close-up I snapped at Tyler Arboretum in Media, PA. This is their signature tree, the same one that my wife was standing under in the photo in this post. I kept this one at full resolution - it makes for a great desktop wallpaper.
The bark of a Giant Sequoia is like that of few others. It's light, fibrous, and can be up to two feet thick at the base. These qualities make it a poor conductor of heat. That, and its fire resistance help protect the sapwood from damage when surrounded by fire. These fires are actually good for a large Sequoia -- they help dry up and open the cones that may stay green and hang in the tree for up to twenty years. This is perfect timing - the newly released seeds will have a new forest floor to take root in.