如何将x轴标在水平线上旋转90度

I'm trying to visualize a correlation map, and I think that I've gotten it to work, except for the jumbling of the x-axis labels. Any suggestions for how to rotate them? Some of the parameters for many of the Base R plots don't seem available for levelplots. It's possible that I don't know what I'm talking about.I'm trying to visualize a correlation map, and