You can learn CS 101-type C pretty quickly by eliminating pointers/structs/etc., but you won't be able to read/alter any real-world open source C. If you learn Python or Ruby, for example, you can jump into github and see what people are doing right now.
If you're looking for an ancestor language, you'd be just as well off learning Smalltalk, which you can do real things with immediately (e.g. learn it in the browser with Seaside), and then apply those lessons to modern languages like Obj-C and Ruby.