Well, I can definitely see that one, but I have no idea what it is. I'm pretty good with native tree species, but I suspect this is not a native. A lot of the trees in the Henninger Flats area are introduced species.
One of the reasons I'm good at identifying native tree species is that there aren't that many of them.
Native Tree Species in the greater LA area:
Oaks
1. Coast Live Oak
Quercus Agrifolia
2. Valley Live Oak
Quercus Lobata
3. California Black Oak
Quercus Kelloggii
4. Canyon Live Oak
Quercus Chrysolepis
There area also a number of other members of the quercus genus locally, but they are generally regarded as scrub oaks and not trees.
Conifers
1. Big Cone Douglas Fir
Psuedotsuga Macrocarpa
2. Coulter Pine
Pinus Coulterii
3. Singleaf Pinyon
Pinus Monophyla
4. Sugar Pine
Pinus Lambertiana
5. Limber Pine
Pinus Flexilis
6. Lodgepole Pine
Pinus Contorta
7. Jeffery Pine
Pinus Jefferii
8. Ponderosa Pine
Pinus Ponderosa
9. Utah Juniper
Juniperus Osteopsperma (I believe that's our local species. I might verify that when I get home.)
10. Incense Cedar
Calocedrus Decurrens
11. White Fir
Abies Concolor
12. Digger Pine (aka Gray Pine)
Pinus Sabiana
Misc
1. California Black Walnut
Can'tus Rememberus -- Juglans I think is the genus
2. Hollyleaf Cherry
Prunus Illicifolia
3. California Bay Laurel
Umbelularium Californica
4. Big Leaf Maple
Acer Macrophylum
5. Fremont Cottonwood
Populus Fremontii (I may be mistaken about the species, and there may be 2 species locally)
6. Sycamore
Plantanus Racemosa (not sure about the common species name for our local sycamore trees)
7. White Alder
Alnus Rhombofolia
8. Mexican Elderberry
Sambucus Caerulea
-There are also a number of native willow species, some of which grow to tree like proportions but are not generally regarded as tree species.
-There are also rarer species like the Catalina Cherry or the Torrey Pine that I'm not going into. I'm trying to cover what one would normally see in the Front Ranges and High Country of the local mountains.
Lastly, don't take my Latin declensions as gospel. I often will make declension errors like macrophyla when I mean macrophlum and the like.
4 oaks + 12 conifers + 8 misc = 24. I've probably missed a couple since I'm doing this off the top of my head, but you get the idea: They're aren't that many native tree species, so identification isn't that bad.