Country rock (geology) in geology when the term "country rock" is used include: When describing a pluton or dike, the igneous rock can be described as intruding the surrounding "country rock", the rock into which the pluton has intruded. When country rock is intruded by dyke, it is called "discordant intrusion," while intrusion by a sill indicates a "sub-parallel" or "concordant intrusion". Most intrusions into country rock are via magma. Usually, country rock is intruded by an igneous body of rock which formed when magma forced upward through fractures, or melted through overlying rock. Magma then cooled into solid rock, different from the
Boring Lava Field Quaternary, in what is now the Portland area as well as the surrounding area, with a particularly concentrated pocket of activity to the east. Nearly all of these eruptions were confined to single vents or small vent complexes, with the exception of a lava plain southeast of present-day Oregon City. Boring Lava generally consists of flowing lava; only one eruptive deposit contains tuff, ash, and tuff breccia, and one vent to the northeast of the Carver area displayed evidence of explosive eruptions that later became effusive. According to the United States Geological Survey, sometime less than 100,000 years ago, magma