INCOME TAXES - Deferred Tax Assets and Liabilities (Details) - USD ($)	12 Months Ended
	Dec. 28, 2019	Dec. 29, 2018
Federal:
Current	$ (66,000)	$ (387,000)
Deferred	(3,449,000)	(1,454,000)
State:
Current	3,000	1,000
Deferred	(804,000)	(345,000)
Total	(4,316,000)	(2,185,000)
Benefit for income taxes	5,396,000	2,500,000
Provision for income taxes	$ 1,080,000	$ 315,000
Difference between tax rate for continuing operations on income or loss for financial statement purposes and federal statutory tax rate
Statutory tax rate (as a percent)	(21.00%)	(21.00%)
Percentage depletion		(0.90%)
Non-deductible expenses (as a percent)	0.10%	0.40%
Valuation allowance for tax assets (as a percent)	0.50%	1.20%
State income taxes, net of federal benefit (as a percent)	(4.50%)	(4.50%)
Other (as a percent)	1.20%	(2.40%)
Total (as a percent)	(23.70%)	(27.20%)
Current statutory federal and states tax rates (as a percent)	25.74%
Deferred tax assets
Reserves for self-insured losses	$ 417,000	$ 466,000
Accrued reclamation	1,972,000	1,445,000
Unfunded supplemental profit sharing plan liability	431,000	263,000
Asset valuation reserves	439,000	685,000
Future state tax credits	833,000	833,000
Net state operating loss carryforwards	812,000	226,000
Federal AMT carryforward	116,000	387,000
Federal NOL carryforward	3,226,000	468,000
Other	939,000	700,000
Total deferred tax assets	9,185,000	5,473,000
Deferred tax liabilities
Depreciation	833,000	1,200,000
Deferred development		116,000
Other	285,000	443,000
Total deferred tax liabilities	1,118,000	1,759,000
Net deferred tax asset before valuation allowance	8,067,000	3,714,000
Beginning balance	(300,000)	(200,000)
(Increase) decrease during the period	100,000	100,000
Ending Balance	(400,000)	(300,000)
Net deferred tax asset	$ 7,667,000	$ 3,414,000