Name spelling. In Germany the name would have been spelled Holtzkau. It appears as Holtzclaw among the Virginia pioneer family, and seems to have been modified to Holsclaw as the family moved to Missouri.
The latter went to California with Milton, son of James Holsclaw, a pioneer of Gilroy, CA, in 1851. Actually Milton was accompanied by his brothers Clifton and James P. in 1849, to the gold fields near Diamond Springs, CA. Both of his brothers served during the CA Indian troubles, but Milton did not. Clifton and James P. were back in Missouri for the 1860 census.