Girl Scout Encampments were held regularly - my guess is yearly except for years with Roundups, but I have yet to find information on each year. Size of the encampment seems to have been limited to around 110 Seniors, but some years it is noted that fewer attended. The Participants listing in the April 1967 Leader's magazine notes that the Seniors need to have completed 10th or 11th grade, but have no previous national or international opportunity. Rangers (Girl Guides from Canada of equal age) were also invited. It is assumed that an equal number of boys from a "cooperating organization" attended. Encampments were different from Round-ups. Encampments were held more often, space was limited to fewer girls, and at times Seniors camped without adult supervision (!).
Girl Scout All-State Encampment List
1951 - Cody, Wyoming, August
(International Encampment held at Camp Wind Mountain, Washington in July '51)
1952 - Unknown
1953 - Unknown
1954 - Buffalo Bill Youth Camp at Wapiti, near Cody, Wyoming - unknown if this site was used for other Encampments.
1955 - Cody, Wyoming
1956 - (may not have been held due to Roundup?)
1957 - (World Encampment held at Doe Lake, Ontario, Canada, August 10-19)
1958 - San Bernadino Mountains, California
1959 - Unknown (may not have happened due to Roundup?)
1960 - First Wilderness Camp (All-States) at Deschutes National Forest, Oregon
1961 - Todd Lake, Oregon, also Camp Ross, Ohio, also somewhere in Michigan.
1962 - Camp Tocanja near Muskegan, Michigan
1963 - California, Michigan & Maryland
1964 - Conowingo, Maryland
Emigrant Gap, California
1965 - Nantahala National Forest, North Carolina (Special note - Seniors went backpacking without adults for several days)
1966 - Nantahala National Forest, North Carolina
1967 - Nantahala National Forest, North Carolina (105 Seniors attended, backpacking without adults).
1968 - Boxwood State Forest near Middleton, Massachusetts. Limited to 110 Senior .
Source of information: Historical Record of Girl Scouting in Pierce County by Mrs. Robin Otis. Leader's Magazine April 1967, June 1967, November 1966. And The Fence Came Down by Maienchein & Neiler