SACRAMENTO, Calif.—California’s health director on Tuesday revealed the math behind the state’s calculation that it was safe to lift all remaining stay-at-home orders, a response to criticism that Gov. Gavin Newsom’s administration was hiding key data affecting people’s lives and livelihoods. A half-dozen formulas were used to project that all regions of the state will top 15 percent capacity in their hospital intensive care units in four weeks, a level the state believes provides adequate cushion for any surges in virus patients. Southern California and the San Joaquin Valley currently have 0 percent capacity when taking into account both coronavirus cases and other patients, while rural far Northern California is the only one of five regions above the minimal level. A surge that started in mid-October made California the nation’s COVID epicenter before numbers improved in the new year. Four regions accounting for virtually all the state’s nearly 40 million …