As Leno says as he turns down Laurel Canyon, "I don't think these roads have been resurfaced since, well, probably at least the '80." (My guess would be much earlier, since Laurel Canyon at that point is concrete, which L.A. no longer seems to use.)
Leno's comparison of his backyard loop to Germany's famed Nürburgring is wishful thinking, at best. But in fact, Los Angeles County does have an unofficial race circuit of sorts hidden within its borders: the Angeles Crest Highway—recently reopened after closure due to the 2009 Station Fire. And the surface is in much better condition.
ADDENDUM: According to this recent post from Curbed L.A., which I discovered after logging this entry. The Sunset Strip's concrete (from the 1930s!) will soon be getting a much needed re-surfacing. Leno will be thrilled.