One kind has a trunk with thorns like a rose bush–but much larger. (At one building I’ve noticed that the groundskeeper cut the thorns off where passersby approach the tree.) And the leaves are similar to the leaves on a peach tree.
Another kind is sort of cork-barked–I saw one on the line between a customer’s yard and that of a neighbor; it had been there some 40 years.
Any Dopers know the names of these trees?
We’ll need more info than that to give you any good answers–what region do these trees grow in, what do the flowers (if any) look like, and so forth.
That said, I’ll take a wild stab at your thorny tree. Could it be a black locust?
Miserable nasty trees–the thorns will punch through a steel-belted radial, let alone sneaker soles, and are sometimes covered with an irritating toxin. I’ve seen thorns close to 6 inches on a few trees in Louisiana.
I don’t think that’s it, Balance. I clicked that link and the black locust tree has branches that are thorny, not the trunk. (For the record, I live in Southern California; the thorny-trunk trees–the trunk also bellies out a little between the ground and the lowest boughs–grow in an industrial-park area in Harbor City, near the harbor. The tree with corklike bark grew in the Gardena area, a few miles from my home, near Rosecrans and Vermont avenues–an area about 15 miles south of downtown Los Angeles. (The corky bark is deceptive; when the tree was felled the trunk turned out to be really hard to saw apart.)
Well it sounds like a mesquite tree to me, I have one in my yard and there are huge thorns sticking out of the trunk. I am from Arizona at least some of the time. I would do a google search and try mesquite and see if they have a picture
Locust trees often have thorns on the trunk as well, but I wouldn’t expect to find them in SoCal. It sounds like it might still be some kind of acacia, though. I haven’t turned up any good pictures of SoCal acacia varieties, mainly because people seem prone to naming their streets and apartment complexes after the bloody things.
I can’t even offer a hint on the other tree species just yet.
(Mesquite is another variety of acacia–they tend to be low, kind of shrubby plants.)
I’m sorry, Phlosphr. I did a Google search for “Mesquite+tree”; it showed a tree but the description said nothing about a thorny trunk. It mentioned flowers, but the trees I see all the time don’t seem to have any. And the site’s description of the leaves didn’t match the leaves I saw, as noted in the OP. A variation, perhaps…
Here’s a picture ( which I personally wouldn’t pay money for ) of a Honey Mesquite’s ( Prosopis glandulosa )branches:
http://www.azemporium.com/images/imagepages/Johnston/pjhoneymesquite.htm
Notice it has paired stipular spines.
Whatever it is it likely is some sort of Faboid ( pea ). Acacias, Locusts, and Mesquites are all related Faboid plants and all are commonly planted ornamentals in SoCal. And Balance is right that the damn prolific locusts ( I just pulled up several seedling out of my lawn today 
) in front of my house have a few spines on the trunk, though they’re not real large. Does this tree completely lack spines on the branches? That’d be weird - Not sure what too look for if that’s the case.
The cork-bark one I’m still mulling over 
.
- Tamerlane
Floss Silk or Silk Floss tree? Has a thorny trunk which bulges out with age, and is planted as an ornamental in So Cal:
http://www.desert-tropicals.com/Plants/Bombacaceae/Chorisia_speciosa.html
http://www.gardenfla.com/databasepages/chorisia.htm
http://www.csupomona.edu/~srkoukol/bot124lab/treewalk/chorisia.html
If it flowers, or produces seed pods with silk in them, that could be your tree.
Oh, hey here’s a Desert Peach ( Prunus andersonii ):
http://eco.bio.lmu.edu/socal_nat_hist/plants/photos/large/prun_an2.jpg
It’s just a shrub, but notice the longish spines ( actually modified twigs in this case ). If it looks like this it might be a member of this genus ( i.e. it might actually be closely related to a Peach tree ).
- Tamerlane
Burr Oak? They withstand fires by having a thick layer of bark, and oak is a hardwood.
Hawthorn? They look like a fowering crab, but are covered in thorns.
Hey, that looks like it, Yabob! Thanks! Including the “bottle shaped” trunk…as for the flowers, I guess I’ll have to wait and see what happens when the honeywind blows…