Complex sentence: The Glades I culture, lasting from 500 BCE to 800 CE, was apparently focused around Gordon Pass and is considered the least sophisticated due to the lack of artifacts, and what has been found--primarily pottery--is gritty and plain.
Split into simpler sentences: The Glades I culture, lasting from 500 BCE to 800 CE, was apparently focused around Gordon Pass and is considered the least sophisticated due to the lack of artifacts. What has been found--primarily pottery--is gritty and plain.