To go with the post on pay for senior archaeologists in the US this post looks at what is takes to get such a job. Using the requirements listed in the job postings, same as the ones used to determine pay conditions, this post presents the results-
What the graph shows is that there is year to year fluctuations but the requirements to be at the top of CRM in the US has been pretty constant: regional/local experience in your area of work; at least a graduate degree; at least five years of experience. While the mention of 5 years of experience is the most common 10-20 years of experience is become more common. Furthermore, 5 years is a minimum and it does not mean that having five years of experience will insure that you are even considered for a top level job.