I removed mulch and tried to dig up a few inches down

==>> explain how ...

its stressed ... its NOT hungry.. do NOT fert ...

pic of the whole ...

the size of the box doesnt help me understand the size of the tree ... other than big

explain how you planted it ... any amendments??? and any other info ... soil type ...

if its a huge as i think.. if it lived i would be happy .. and not be too worried about it not being pretty ...

a large tree transplant.. can take upwards of 3 years to get established ...

ken

Having planted and killed a 48" box Q. agrifolia in So Cal, I can speak to this.

Firstly,

What is your watering regime for this tree?

What is the location--are you in the foothills, or on the adobe clay coastal plain where drainage is not so instant?

What was the guarantee on the tree?

Is there any difference between the healthy tree and the decliner as far as drainage, watering, shade, surrounding plantings?

Just briefly, a Q. agrifolia planted from a box has significantly different needs than a mature oak, which wants zero summer water to avoid fungal infections.

Yellow leaves are usually a sign of either a lack of nitrogen OR iron. So, how can you which one your plant is deficient in? Well, it is really quite easy.
Monday, we talked about nitrogen deficiency, which causes older leaves to yellow and newer leaves to stay green. However, when it comes to iron deficiency it is the opposite - younger leaves turn yellow first.
The other characteristic of iron deficient plants is that although the younger leaves turn yellow, their veins remain green.
Iron is needed for plants to function. Without it, they will not grow.
What is interesting about iron is that there is usually plenty of it in the soil. BUT, certain factors can affect it being available for plants to absorb. If your soil is wet, has a high pH (alkaline soil), and/or clay soils are all factors that can lead to iron from becoming unavailable for plants.
Iron deficiency is best treated by preventing it from occurring in the first place. If your soil pH is over 7.0, clay-like OR often wet - then incorporate compost and peat moss before planting.
http://www.birdsandblooms.com/blog/yellow-leaves-and-green-veins-iron-deficiency/

Here is a link that might be useful: Iron Chlorosis

Have you ever had a live oak before?

Even though you live in California the live oaks will have its normal leaf drop. They differ from deciduous trees that lose their leaves in the fall all at once, live oaks lose leaves a little at a time in the early spring to late spring, being replaced with new, so you really don't notice.

In California it may not come all at once like in Texas, but probably more like Florida. Where between Feb and June, depending on tree variations you will see leaves turn yellow and drop and replaced by new leaves.

Did your tree already have its annual leaf drop.

We have a very large but young live oak. It’s approx 30 inch in diameter at the base. Approx 30 yrs old according neighbor who has lived 50 years. The older tree is even older. This younger has been showing yellow leaf and leaf drop all year. Started in outer edges. Another tree in neighbors yard showing similar. These trees touch each other at the top on the crown.

start your own post.. add some pix of you tree .. included you big city location ...

and contact your local county extension office.. and ask them if there are any current issues with live oaks in your area .. and report that info back to us ...

ken

SK ..where are you trees located? yellow leaves and leaf drop could be totally normal for a live oak. Sounds like you may have just aquired the property these oaks live on. if you are in florida, south texas its early spring and live oaks do lose and replace leaves during that time. Did you happen to have a cold snap? in general live oaks will also lose leaves during a cold snap. Usually starting at top with smaller branches.