If Column E (CA source) is blank on a CA K-1, you will report the interest income as Colorado source. Interest and dividends are usually sourced to the state of the resident. It is possible for interest to be CA-source, but it is up to the partnership or trust that prepared the K-1 to determine that.
Refer to page 7 California instructions for schedule CA-NR, line 8.
https://www.ftb.ca.gov/forms/2016/16_540nrcains.pdf