The cowboy era finally ended around 1890. which is the simple predicate? cowboy around 1890 finally ended ended

The correct option is ENDED.
A predicate refers to the part of a sentence or a clause which tells what the subject does or is. A predicate is usually made up of a main verb and the verb phrase.
A simple predicate is defined as the main verb in the predicate which tells what the subject does. In the sentence given above, the complete predicate is 'finally ended around 1890 and the simple predicate is 'ended'. This is because, 'ended' is the main verb in the sentence.