Hey, how did you get a picture of my mahonia?

Acyually mine doesn't look that good. I have no idea what the problem is either. Probably some kind of fungus based on the circular spots.

Actually, it looks pretty good. Just the reddish coloration as the leaflets get old.

Is this the first time you've had Mahonia?

Yes, although I've had this plant and one other for a few years. Both were planted from small containers. The other one is almost entirely green.

it doesn't look well to me. i don't think the orange colored leaves are normal, esp. on the upper portions. mine sheds some interior leaves at times but not entire stems like that. i find them to be pretty tough plants and grow them in dry shade.
just a guess but maybe the soil is too aklaline from leaching of the concrete in the house foundation or that site is too wet for it. any standing water there or does the area drain poorly?

Maybe the concrete is an issue, but hard to believe the site is too wet given the drought conditions and the fact that much of the shade is cast from a huge sugar maple.

Mahonias cannot tolerate calcium carbonate which is in most concrete. Perhaps the roots have discovered your foundation. It does look as though only one side of the plant has been affected which would suggest this as the problem.

I can't tell because the photo is too small. Mine normally have red leaves until the warm season... around now they put out new green leaves. I don't believe these do "great" here.
Don't seem to be thriving. Don't see many that are outside of garden center containers. I have M. aquafolium by the way.