What is the word instead of "valley" I have a plot as below, there is a "valley" in it. But I know the word _valley_ is not suitable for my plot which has scientific details. What is the best word for describing the _z_ component behavior versus _x_ and _y_ components? The shape of the valley is shown in the photo at the bottom. ![3-dimensional plot]( ![photograph of glacial valley](

There is nothing wrong with using _valley_ in this context. It is a visual metaphor which will be readily understood.

An alternative word might be _trough_ , which is a bit more common in this abstract sense; but is still a visual metaphor.