Redwood forests are added with the ExtrabiomesXL mod. They commonly have very large redwood trees that can get over 60 blocks tall. They can also have steep cliffs and overhangs.
There is also one type of redwood that is most commonly seen in meadows that grows to be about 200-250 blocks tall. They have a thick outer bark and a wood interior. The bark and Inteiror all give 4 wood when crafted.