If it has bark like a coastal redwood, and foliage like a coastal redwood, and a slender conical structure like a coastal redwood, it is most likely a coastal redwood. If it turns orangish brown in autumn and defoliates through winter, it is the much less common dawn redwood, Metasequoia glyptostroboides. It is one of only a few distinctive genera of coniferous trees that are deciduous.
Upon closer inspection, it is not as similar to coastal redwood as it initially appears. Besides being deciduous, the foliage of dawn redwood is softer and lighter grassy green. Individual leaves are more perpendicular to the stems. Trunks are more tapered, so that they are quite lean up high, and quite plump down low. Old trees can form buttressed trunks. Strips of bark might exfoliate.
Dawn redwood is by no means a deciduous alternative to the evergreen coastal redwood. Although it grows about as fast while young, it slows with maturity. Crowded trees get taller but lanky. Exposed trees stay shorter and broader, but because they are still relatively narrowly conical, they do not make much shade at first. Old trees are more than a hundred feet tall, but could get taller.
No other big tree has trunks as sculptural as those of the California sycamore, Platanus racemosa. They bend and groove so irregularly, seemingly without direction, that it is a wonder that old trees in the wild eventually get a hundred feet tall. Some trees have a few trunks. The mottled beige bark is quite striking both in the shade of the broad canopy, and while trees are bare in winter.
Tony Tomeo 