Complex sentence: By this time, the pre-Christian religious beliefs and mythology were already fading, and the Tongva language was on the brink of extinction by 1900, so that only fragmentary records of the indigenous language and culture of the Tongva have been preserved.
Split into simpler sentences: By this time, the pre-Christian religious beliefs and mythology were already fading. The Tongva language was on the brink of extinction by 1900, so only fragmentary records of the indigenous language and culture of the Tongva have been preserved.