Redwood trees are among the largest living things on earth. There are three genera of redwood: Metasequoia, a deciduous tree found only in a certain valley of China; the Sierra redwood (Sequoiadendron gigantea), an evergreen that grows primarily on the Western slopes of the Sierra Nevada Mountains of California; and the Coast redwood (Sequoia sempervirens), also evergreen, which grow in the coastal ranges of southern Oregon and Northern California. Since I live in Northern California, it is natural that I use only Coast Redwood, which grows in this area, actually right around my house and shop.
Coast redwoods are the tallest trees on earth--they may grow more than 350 feet tall with diameters up to 25 feet. Such dimensions take a thousand or more years to achieve. Trees like that are no longer harvested, but many were cut in the 19th century. Today, redwood harvesting is closely managed to insure the future of the forests and their environment.
Redwood is often categorized as "young-growth" or "old-growth". This distinction occurs primarily because the width of growth rings reduces as the tree's diameter increases. Thus, wood taken from older trees will have a tighter grain pattern. The dividing line between young-growth and old-growth is usually considered to be around 300 years, although it also depends on the growing environment of the tree. Older trees have mostly been harvested in the past, but they are protected today, therefore old-growth lumber is rare. What we have today comes largely from recycled old-growth structures such as water and wine tanks, or from fallen or cut logs still lying in the forests.
Redwood is very resistant to rot and insects, so trees cut 100 years ago and left on the ground, still may contain much good wood today. That is the case in the area where I am located, there are enough old logs to provide all the old-growth lumber I could ever use--the problem is getting them out to be milled. In most cases, these logs are located in places where it was too difficult to remove them at the time of cutting--even today, it is not an easy task.
Redwood is a soft wood. A redwood log has a layer of bark on the outside, which can be several inches to a foot thick. Directly under the bark is the "sapwood", which is a light yellow color in a layer several inches thick. Inside the sapwood is the "heart", which contains wood of the characteristic red color. Old-growth wood tends to be darker than young-growth wood. Both woods darken when exposed to direct sunlight, even for only a few hours. Young-growth, especially, has a relatively light red color when freshly milled; this color does not show the grain patterns very clearly until the wood is darkened by deliberately exposing it to sunlight. This develops the characteristic deep red color without using any stain in the finish.
Since sapwood does not have the rot and insect resistance of heart wood, old logs often consist of entirely heart wood--the bark and sapwood are long gone due to rot, insects, and forest fires.