Prospecting for gold during the California gold rush was a relatively easy task, because of erosion, prehistoric glacier movement, and ancient, gold-bearing riverbeds thrust to the surface by volcanic activity put gold literally within reach for anybody with a pan or shovel.
Option Elimination -
First, a quick clarification on "because of," "because," and "since."
"Because of" is a prepositional phrase that modifies a noun or a pronoun, indicating a cause or reason for something. E.g., He arrived late because of heavy traffic.
"Because" is a subordinating conjunction that introduces a subordinate clause, explaining the main clause's reason or cause. It suggests a stronger relationship between the clauses. E.g., He failed the test because he didn't study. The failure in the main clause is directly attributed to the reason mentioned in the subordinating clause, which is the lack of studying.
"Since" establishes a more general relationship between the main and subordinate clauses. It suggests that the reason in the subordinate clause is a contributing factor but not the necessary sole cause. E.g., Since it was raining, they decided to stay home. The rain mentioned in the subordinate clause is a contributing factor to their decision, but it may not be the only reason. There could be additional reasons not stated in the sentence.
Broadly, we need a "Because" (preferably without a comma) or "Since" to introduce a subordinate clause.
(A) because of erosion, prehistoric glacier movement, and ancient, gold-bearing riverbeds thrust to the surface by volcanic activity put gold literally within reach for - Here the subordinate clause is introduced by a prepositional phrase "because of". We need "Because" (preferably without a comma) or even better "since." Moreover, "within the reach of" is preferred.
(B) because of erosion, prehistoric glacier movement, and volcanic activity that thrust ancient, gold-bearing riverbeds to the surface, and putting gold literally within reach of - "Because of" and "putting" - wrong.
(C) owing to erosion, prehistoric glacier movement, and volcanic activity that had thrust ancient, gold-bearing riverbeds to the surface, and putting gold literally within reach of - "owing to" - prepositional phrase and "putting" - wrong.
(D) since erosion, prehistoric glacier movement, and volcanic activity that thrust ancient, gold-bearing riverbeds to the surface, putting gold literally within reach for - "putting" - wrong
(E) since erosion, prehistoric glacier movement, and ancient, gold-bearing riverbeds thrust to the surface by volcanic activity put gold literally within reach of- Perfect