Searched intensively on Google for "Colorado" and "arrowhead hunting". Eventually found a location for surface hunting. (Private Ranch which leased out camping spaces) They had large areas for isolated arrowhead hunting but was covered with lots of rocks. Made it difficult. Did not find any "digs".
This mornings' WX channel expert calls the Colorado washout a " once in 1,001 years event "... Estimating 1 Billion $ damages. What Indians were living in Colorado 1,001 yrs ago