There is currently a meadowlark singing in Day, Modoc county, CA that appears to be a strong candidate for Eastern. It is singing a song not perfectly typical for Eastern but likely within the range, and certainly a much closer match than a Western. It has also given the classic eastern high buzzy flight call. While it may be that only audio is diagnostic, the bird also has a white malar and extensive white on the tail feathers. Many photos and audio recordings have been attained. I will upload them to an eBird list shortly.
The bird was first heard from here 41.2146298,-121.3775120. It was singing persistently for periods and then silent for periods. It was singing from this field 41.2120852,-121.3787314. It was not excessively responsive to playback. It seemed to be pared with a Western Meadowlark.
If you are in the area consider looking for this bird. There are no accepted records for the state of California so a large amount of documentation would be necessary to establish the record.
Good birding, Logan Kahle San Francisco/Willows, CA