I have a large water color, mostly blue and black. It's a wolf with cattle skulls baying at the moon and a tall palm tree. Is this worth something?

It's worth whatever someone might want to pay for it. I do notice that quite a few of his paintings come up in image searches in Google. Geoffrey Holt watercolor painting - Google Image Search If you click on that and then subsequent links that you will find, I bet that you will find some prices listed for his works that might give you an approximate idea of what yours might possibly be worth in terms of monetary value.

I also notice that there are some selling on eBay. Geoffrey Holt Painting eBay - Google Search