The deciduous leaves are opposite, simple, 3-5" long, dark glossy green, with five lobes which are usually entire but can be undulated. The base of the leaf is often truncated, or flat which is were the name comes from. White milky sap can be seen if you remove the leaves in summer. New spring growth with a reddish cast.
Flowers are small, greenish yellow and look like many other maples in this group (A. platanoides, A. campestre).
Fruit is a pair of samaras, usually broadly spreading into a U shape.
Stems are smooth, as is the bark.
Fall color can be yellow, reds, oranges. This is one I planted many years ago in Spokane.
This species is related to A. platanoides and has been hybridized to produce several commercially available trees including 'Pacific Sunset' and 'Norwegian Sunset'. Both hybrids resulting in a smaller size, better fall color and drought tolerance of A. truncatum.
Most likely looks like a cultivar of A. palmatum around here. But the flowers are a different color.
Other locations where more maples grow you might see A. pictum mono, A. cappadocicum.
Stumbled across this link to cultivars. Wow.
114 Seacliff Dr
204 El Camino Del Mar