NIST - CSRC - Bitcoin is a fork and Bitcoin Cash is the original blockchain

According to NIST National Institute of Standards and Technology - CSRC Computer Security Resource Center:

In July 2017, approximately 80 to 90 percent of the Bitcoin computing power voted to incorporate Segregated Witness (SegWit, where transactions are split into two segments: transactional data, and signature data), which made it possible to reduce the amount of data being verified in each block. Signature data can account for up to 65 percent of a transaction block, so a change in how signatures are implemented could be useful. When SegWit was activated, it caused a hard fork, and all the mining nodes and users who did not want to change started calling the original Bitcoin blockchain Bitcoin Cash (BCC). Technically, Bitcoin is a fork and Bitcoin Cash is the original blockchain. When the hard fork occurred, people had access to the same amount of coins on Bitcoin and Bitcoin Cash.

Blockchain Technology Overview - page 41 of 57:

Blockchain Technology Overview

Source: https://csrc.nist.gov/CSRC/media/Publications/nistir/8202/draft/documents/nistir8202-draft.pdf

Wayback Machine: https://web.archive.org/web/20180129042518/https://csrc.nist.gov/CSRC/media/Publications/nistir/8202/draft/documents/nistir8202-draft.pdf

Nandibear.com PDF: https://nandibear.com/docs/bitcon-is-a-fork-and-bitcoin-cash-is-the-original-blockchain-nist-csrc-national-institute-of-standards-and-technology-computer-security-resource-center-nandibear.com-luke-2018-nistir8202-draft.pdf