The data used in Paciorek and Schervish (2004). This is a data.frame with 3 columns, columns 1 and 2 corresponds to the predictors and column 3 corresponds to the target.
Paciorek, C. J. and Schervish, M. J. 2004. "Nonstationary Covariance Functions for Gaussian Process Regression". In Thrun, S., Saul, L., and Scholkopf, B., editors, Advances in Neural Information Processing Systems 16. MIT Press, Cambridge, MA.