This guidebook, Hydrogeology of Trans-Pecos Texas, grew out of our interest in the hydrogeology of desert environments. After we participated in Marty Mifflin and Jay Quade's 1988 field trip through eastern Nevada; we realized that, although there were many similarities, the hydrogeology of Trans-Pecos Texas was quite different from what we had observed in Nevada. Thus the seed was planted for this field trip and guidebook.

Horizontal drilling in a mature hydrocarbon province such as Texas can increase recovery from reservoirs in which a significant proportion of oil or gas in place remains unrecovered by conventional means. Such drilling has been particularly effective in increasing production where production is from natural fiactures, such as in the Pearsall field of the Austin Chalk trend in South Texas. Production can also be enhanced where the reservoir-quality