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The basal Cambrian Hickory Sandstone marks the beginnings of Paleozoic sedimentation in Central Texas. It is a bimodal well rounded, poorly sorted, fine and coarse sandstone. About half the samples are orthoquartzites, the remainder being divided between subarkose and quartzose subgraywacke. Well developed cross-beds in the lower Hickory exhibit a very uniform southeasterly direction, and were produced by marine currents controlled by northwest-southeast Pre-Cambrian ridges on a southeast paleoslope. Metamorphic quartz increases to the southeast. Approximately 75% of the feldspar found is orthoclase; the remainder is twinned microcline. The Hickory Sandstone is largely marine, but was derived from desert dune sands which were in turn derived from the Llanoria land mass to the southeast and the Texas Craton to the northwest

The Ortiz Mountains lie in a belt of early Tertiary intrusive centers adjacent to the Rio Grande depression of north-central New Mexico. Tertiary organic activity and subsequent erosion have etched this mountain group into considerable relief. Intrusive activity occurred during early Tertiary Espinaso time and resulted in emplacement of sills and dikes of a central stock. Correlation of volcanism with intrusive phases is difficult. Most volcansim probably occurred during the later part of Ortiz igneous activity. An elongate vent is exposed in the eastern part of the mountains and structurally occupies the highest position in the group. The principle igneous rocks of the Ortiz Mountains are mazonite, latite-andesite porphyry, and latite porphyry. Of these, latite-andesite porphyry probably is the oldest. Outcrops of this rock are found flanking the mountains on all sides. Sills extend from laccolithic and plug-like intrusive centers and occur along many different horizons of the Upper Cretaceous rocks in the area. Intrusion of the central stock followed the latite-andesite porphyry. The stock rock is nepheline-bearing augite monzonite. Volcanism probably followed intrusion of the stock. The vent rock is latite porphyry that exhibits intense hydrothermal alteration. Small plugs of quartz-bearing mozonites may have been intruded contemporaneously with latite porphyry. Post-Espinaso faulting resulted in development of the Tijeras-Golden fault system which cuts the southern part of the Ortiz Mountains. The Ortiz Mountains probably were a highland area of subdued relief in middle Miocene time. Considerable rejuvenation of the areas occurred during the development of the Rio Grande depression in the Pliocene. Uplift of the area is reflected by strong eastward tilting of the sedimentary rocks. Erosion cut the lower Ortiz surface by latest Pliocene time. Gravel accumulation on this surface continued into the Pleistocene. The cuesta topography along the northern flank of the mountains may be the result of minor Quaternary faulting.

The Precambrian metamorphosis rocks of the Tijeras Canyon area crop out along a five-mile, northeast-trending belt, which lies approximately five miles east of the Sandia Mountains front, in north-central New Mexico. The sequence, to the east, is overlain uncomfortably by Pennsylvanian Madera limestone, while the trace of the Tijeras fault marks the western side.