INCOME TAXES (Tables)

12 Months Ended

Dec. 31, 2019

A summary of the provision for income taxes is as follows (in thousands):



	Year Ended December 31,
	2019		2018		2017
Current portion of income tax expense (benefit):
Federal	$	—	$	23	$	(2,793	)
State	53		85		10
Deferred portion of income tax expense:
Federal	—		—		—
State	—		—		—
Total income tax expense (benefit)	$	53	$	108	$	(2,783	)

Reconciliation of The Statutory Rate to The Effective Rate

A reconciliation of the federal statutory income tax rate of 21% for 2019 and 2018, and 35% for 2017 to our effective rate is as follows (in thousands, except percentages):



	Year Ended December 31,
	2019			2018			2017
Federal taxes at statutory rate	$	2,874		$	2,497		$	(8,873	)
Add:
State taxes, net of federal benefit	1,245			1,663			(1,414		)
Change in valuation allowance	(6,754		)	(3,330		)	(104,710		)
Change in federal and state tax rates	2,322			634			115,545
Percentage depletion	(600		)	(656		)	(598		)
Other	966			(700		)	(2,733		)
Net expense (benefit) as calculated	$	53		$	108		$	(2,783	)

Effective tax rate	0.4		%	0.9		%	11.0		%

Schedule of Net Deferred Tax Assets and liabilities

Significant components of our deferred tax assets and liabilities were as follows (in thousands):



	December 31,
	2019			2018
Deferred tax assets (liabilities):
Property, plant, equipment and mineral properties, net	$	133,586		$	138,855
Federal and state net operating loss carryforwards	63,194			65,779
Asset retirement obligation	5,763			5,950
Deferred revenue	4,371			3,035
Other	2,839			2,888
R&D credits	1,870			1,870
Total deferred tax assets	211,623			218,377
Valuation allowance	(211,623		)	(218,377		)
Deferred tax asset, net	$	—		$	—